Combined early downlink and uplink synchronization for l1 / l2-triggered mobility (LTM)

Abstract

Embodiments include methods for a user equipment (UE) configured for layer-1 / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN). Such methods include receiving, from a RAN node, a single command for early synchronization with an LTM candidate cell. The single command includes an identifier of the LTM candidate cell and an identifier associated with a transmission configuration indicator (TCI) state of the LTM candidate cell. Such methods include, based on the single command, performing early uplink (UL) synchronization and early downlink (DL) synchronization with the LTM candidate cell. Other embodiments include complementary methods for a RAN node, as well as UEs and RAN nodes configured to perform such methods.

Description

[0001] COMBINED EARLY DOWNLINK AND UPLINK SYNCHRONIZATION FOR L1 / L2-TRIGGERED MOBILITY (LTM)

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to wireless networks, and more specifically to techniques for improving conditional and non-conditional layer-l / layer-2 triggered mobility (LTM) of user equipment (UEs) across multiple cells in a radio access network (RAN), such as in relation to UE early downlink (DL) and uplink (UL) synchronization with LTM candidate cells.

[0004] BACKGROUND

[0005] The fifth generation (5G) of cellular systems has been standardized within the Third- Generation Partnership Project (3GPP). 5G was developed for maximum flexibility to support various use cases including enhanced mobile broadband (eMBB), machine type communications (MTC), ultra-reliable low latency communications (URLLC), side-link device- to-device (D2D), and several others. 5G was initially specified in 3GPP Release 15 (Rel-15) and continues to evolve through subsequent releases.

[0006] Figure 1 shows an exemplary 5G network architecture, including a next-generation radio access network (NG-RAN, 199) and a 5G core network (5GC, 198). The NG-RAN may include one or more gNodeB’s (gNBs) connected to the 5GC via one or more NG interfaces, such as gNBs (100, 150) connected via respective interfaces (102, 152). More specifically, the gNBs can be connected to one or more Access and Mobility Management Functions (AMFs) in the 5GC via respective NG-C interfaces and to one or more User Plane Functions (UPFs) in 5GC via respective NG-U interfaces. The 5GC can include various other network functions (NFs), such as Session Management Function(s) (SMF).

[0007] In addition, the gNBs can be connected to each other via one or more Xn interfaces, such as Xn interface (140) between gNBs (100, 150). The radio technology for the NG-RAN is often referred to as “New Radio” (NR). With respect to the NR interface to UEs, each of the gNBs can support frequency division duplexing (FDD), time division duplexing (TDD), or a combination thereof. Each of the gNBs can serve a geographic coverage area including one or more cells and, in some cases, can also use various directional beams to provide coverage in the respective cells. In general, a downlink (DL) “beam” is a coverage area of a network-transmitted reference signal (RS) that may be measured or monitored by a UE.

[0008] As defined by 3 GPP, two DL RS have a quasi -colocation (QCL) relation when the respective antenna ports on which they are transmitted are configured such that properties of a channel over which the RS on one antenna port is conveyed can be inferred from the channel over which a RS on the other antenna port is conveyed. The RAN can indicate to a UE that two antenna ports are QCL with respect to a certain parameter, so the UE can estimate that parameter based on one of the antenna ports and use that estimate when receiving from the other antenna port. More specifically, the RAN can configure with the UE with multiple transmission configuration indicator (TCI) states, with each TCI state providing QCL information that the UE can use to receive a target RS. A TCI state may define a QCL source RS, such that the TCI state itself may be referred to as a QCL source. Once configured, a TCI state is activated by the RAN sending the UE a TCI state activation medium access control (MAC) control element (CE).

[0009] NG-RAN logical nodes (e.g., gNB 100) include a Central Unit (CU or gNB-CU, e.g., 110) and one or more Distributed Units (DU or gNB-DU, e.g., 120, 130). CUs are logical nodes that host higher-layer protocols and perform various gNB functions such controlling the operation of DUs. DUs are decentralized logical nodes that host lower layer protocols and can include, depending on the functional split option, various subsets of the gNB functions. Each CU and DU can include various circuitry needed to perform their respective functions, including processing circuitry, communication interface circuitry (e.g., transceivers), and power supply circuitry. A gNB-CU connects to one or more gNB-DUs over respective Fl logical interfaces (e.g., 122 and 132 shown in Figure 1).

[0010] Seamless mobility is a key feature of 3GPP radio access technologies (RATs). In general, a RAN (e.g., NG-RAN) configures a UE to perform and report radio resource management (RRM) measurements to assist network-controlled mobility decisions, such as for handover from a serving cell to a neighbor cell. Seamless handovers ensure that the UE moves around in the coverage area of different cells without excessive interruption to data transmission.

[0011] Even so, handover and other mobility procedures can have various problems related to robustness. For example, a HO command is normally sent when the radio conditions for the UE are already quite bad, such as at or near cell borders. As such, the HO command may need to be segmented (e.g., to allow for redundancy to protect against errors) and / or retransmitted one or more times before it reaches the UE. In such case, the HO command may not reach the UE in time (or at all) before the degraded connection with the source node (e.g., the node hosting the UE’s current serving cell) is dropped. Failure of handover to a target cell may lead to the UE declaring radio link failure (RLF) in the source cell.

[0012] To address various difficulties with handovers and other mobility procedures, 3 GPP Rel- 16 includes support for conditional handover (CHO) and SN-initiated intra-SN conditional PSCell change (CPC) procedures while Rel-17 includes support for various other conditional mobility procedures. A main principle of conditional mobility is separation of transmission and execution of a mobility (e.g., handover) command. This allows the mobility command to be sent earlier to UE when the radio conditions are still good, thus increasing the likelihood that it is successfully transferred. The execution of the mobility command is done at later point in time based on an associated execution condition.

[0013] Conditional mobility procedures are based on a conditional reconfiguration framework in which the network provides a UE with one or more reconfigurations, each with associated execution condition(s). Each reconfiguration can be provided in an RRCReconfiguration message (in 5G) or an RRCConnectionReconfiguration message (in fourth-generation LTE). When the UE later detects the execution condition(s) associated with one of the earlier-received reconfigurations, the UE executes the associated reconfiguration to perform the mobility procedure (e.g., HO, PSCell change, PSCell addition, etc.).

[0014] Even so, conditional (e.g., CHO) and non-conditional (e.g., HO) mobility operations are triggered by layer 3 (L3) measurements and involves radio resource control (RRC) signaling to change primary cells as well as to release / add secondary cells as needed. Moreover, conventional inter-cell mobility involves complete layer 2 (L2) and layer 1 (LI) resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching.

[0015] 3GPP Rel-18 includes new mobility procedures that facilitate serving cell changes via L1 / L2 signaling to address these problems and / or difficulties. These new procedures are often referred to as L1 / L2 based inter-cell mobility or L1 / L2 triggered mobility (LTM). In LTM, a UE is pre-configured by its serving RAN node with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration.” Each LTM candidate cell configuration may be accompanied by a MAC CE that triggers early TCI state activation for the LTM candidate cell, whereby the UE acquires early DL synchronization. The UE performs measurements on configured LTM candidate cells and transmits corresponding measurement reports to the RAN node, based on which the RAN node triggers execution of an LTM cell switch procedure by the UE to one of the configured LTM candidate cells. The RAN node may trigger the LTM cell switch by sending the UE an LTM cell switch command, including an identifier of an earlier-activated TCI state that the UE should use after the cell switch.

[0016] There are some notable differences between Rel-18 LTM and conditional L3 mobility. For example, unlike conditional L3 mobility in which a UE initiates execution, LTM is initiated by a UE’s serving RAN node based on measurements reported by the UE. This introduces some amount of delay in an LTM cell switch. To capture advantages of both LTM and conditional L3 mobility, 3GPP Rel-19 will introduce conditional LTM (CLTM). Much like conditional L3 mobility, when a UE detects execution condition(s) associated with an earlier-received LTM candidate cell configuration, the UE executes an LTM cell switch to the candidate cell. SUMMARY

[0017] In both LTM and CLTM, a UE performs both early DL synchronization (discussed above) and early UL synchronization, whereby the UE acquires a timing advance (TA) for the LTM candidate cell. Currently, however, a UE receives two separate messages for early UL / DL synchronization: a TCI state activation MAC CE for DL synchronization and a PDCCH order for TA acquisition. Even so, the same beam (e.g., SSB index) in an LTM candidate cell is often associated with both TA acquisition and TCI state activation, e.g., for joint UL and DL TCI states. As such, sending the UE two messages about the same beam wastes scarce signaling resources.

[0018] An object of embodiments of the present disclosure is to improve early DL and UL synchronization for LTM (including CLTM), such as by providing, enabling, and / or facilitating solutions to exemplary problems summarized above and described in more detail below.

[0019] Embodiments include methods (e.g., procedures) for a UE configured for LTM in a radio access network (RAN, e.g., E-UTRAN, NG-RAN).

[0020] These exemplary methods include receiving, from a RAN node, a single command for early synchronization with an LTM candidate cell. The single command includes an identifier of the LTM candidate cell and an identifier associated with a TCI state of the LTM candidate cell. These exemplary methods also include, based on the single command, performing early UL synchronization and early DL synchronization with the LTM candidate cell.

[0021] In some embodiments, the identifier associated with the TCI state is a TCI state ID and performing early DL synchronization with the LTM candidate cell includes activating, for the LTM candidate cell, a TCI state that is identified by the TCI state ID.

[0022] In other embodiments, the identifier associated with the TCI state is an identifier of a RS of the LTM candidate cell and performing early DL synchronization with the LTM candidate cell includes the following operations:

[0023] • selecting, for the LTM candidate cell, a configured TCI state that has a QCL source RS that matches or corresponds to the identified RS; and

[0024] • activating the selected TCI state.

[0025] In some of these embodiments, the identifier of the RS is a synchronization signal / PBCCH block (SSB) index or a channel state information (CSI) RS resource identifier.

[0026] In some embodiments, the identifier associated with the TCI state is a TCI state ID and performing early UL synchronization to the LTM candidate cell includes the following operations:

[0027] • selecting a RS, of the LTM candidate cell, that matches or corresponds to a QCL source RS for the TCI state identified by the TCI state ID;

[0028] • selecting, for the LTM candidate cell, one or more RA parameters that are associated with the selected RS; and • transmitting a RA preamble towards the LTM candidate cell in accordance with the selected RA parameters.

[0029] In other embodiments, the identifier associated with the TCI state is an identifier of a RS of the LTM candidate cell and performing early UL synchronization to the LTM candidate cell includes the following operations:

[0030] • selecting, for the LTM candidate cell, one or more RA parameters that are associated with the identified RS; and

[0031] • transmitting a RA preamble towards the LTM candidate cell in accordance with the selected RA parameters.

[0032] In some of these embodiments, the early UL synchronization and the early DL synchronization are performed responsive to the single command.

[0033] In other of these embodiments, the early UL synchronization is performed responsive to the single command and also includes receiving an indication that the early UL synchronization to the LTM candidate cell was successful. In such case, the UE performs the early DL synchronization in response to the received indication.

[0034] Other embodiments include exemplary methods (e.g., procedures) for a RAN node configured to facilitate LTM by UEs. In general, these exemplary methods may be complementary to the exemplary methods for a UE summarized above.

[0035] These exemplary methods include sending, to a UE via a source cell provided by the RAN node, a single command for early synchronization with an LTM candidate cell. The single command includes an identifier of the LTM candidate cell and an identifier associated with a TCI state of the LTM candidate cell. The single command facilitates both early UL synchronization and early DL synchronization of the UE with the LTM candidate cell.

[0036] In some of these embodiments, the early UL synchronization and the early DL synchronization of the UE are responsive to the single command.

[0037] In other of these embodiments, the early UL synchronization of the UE is responsive to the single command and these exemplary methods also include sending to the UE an indication that the early UL synchronization to the LTM candidate cell was successful. In such case, the early DL synchronization of the UE is responsive to the indication.

[0038] Various embodiments of the exemplary methods summarized above can include various features summarized below. In some embodiments, In some embodiments, the single command is one of the following:

[0039] • a medium access control (MAC) control element (CE);

[0040] • a MAC protocol data unit (PDU);

[0041] • a physical DL control channel (PDCCH) order; • a lean radio resource control (RRC) message;

[0042] • a layer-2 signaling message; or

[0043] • a layer- 1 signaling message.

[0044] In some of these embodiments, the MAC PDU includes first and second MAC CEs, the first MAC CE corresponds to a command to perform early UL synchronization, and the second MAC CE corresponds to a command to perform early DL synchronization.

[0045] In other of these embodiments, the single command is a MAC CE for early DL synchronization and one of the following indicates that the UE should also perform early UL synchronization in response to the MAC CE: a format of the MAC CE, a logical channel or logical channel group associated with the MAC CE, or content of a field in the MAC CE.

[0046] In other of these embodiments, the single command is a PDCCH order for early UL synchronization and one of the following indicates that the UE should also perform early DL synchronization in response to the PDCCH order: a format of the PDCCH order, or content of a field in the PDCCH order.

[0047] Other embodiments, variants, and features of the exemplary methods summarized above are described herein. Other embodiments include UEs (e.g., wireless devices) and RAN nodes (e.g., base stations, eNBs, gNBs, ng-eNBs, etc.) configured to perform operations corresponding to any of the exemplary methods described herein. Other embodiments include non-transitory, computer-readable media storing program instructions that, when executed by processing circuitry, configure such UEs and RAN nodes to perform operations corresponding to any of the exemplary methods described herein.

[0048] These and other embodiments described herein may provide various advantages and / or benefits. For example, by providing a single command that triggers early UL and early DL synchronization, embodiments may reduce L1 / L2 signaling overhead associated with LTM / CLTM procedures. Moreover, by using a single command, embodiments may facilitate more timely UE LTM execution by reducing and / or eliminating duplicative operations (e.g., SSB processing) needed for both early UL and early DL synchronization. In other words, the UE may perform a single operation in response to a single command, thereby reducing and / or eliminating the delay associated with duplicative operations responsive to multiple commands. At a high level, embodiments may facilitate mobility without connection interruption, excess signaling overhead, and excess UE energy consumption.

[0049] These and other objects, features, and advantages of embodiments of the present disclosure will become apparent upon reading the following Detailed Description in view of the Drawings briefly described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 shows an exemplary 5G network architecture.

[0051] Figure 2 shows exemplary 5G user plane (UP) and control plane (CP) protocol layers.

[0052] Figure 3 shows an ASN.l data structure for an exemplary RRC TCI-State information element (IE).

[0053] Figure 4 shows an exemplary TCI state activation MAC CE.

[0054] Figure 5 shows a signaling diagram for an exemplary LTM cell switch procedure.

[0055] Figure 6 shows an exemplary RRC CandidateXcI -State information element (IE).

[0056] Figure 7 shows an exemplary RRC CandidateXcI-UL-State IE.

[0057] Figure 8 shows an exemplary RRC LTM-Candidate IE.

[0058] Figure 9 shows an exemplary LTM candidate cell TCI state activation / deactivation MAC CE.

[0059] Figure 10 shows a flow diagram of an exemplary method for a UE (e.g., wireless device), according to various embodiments of the present disclosure.

[0060] Figure 11 shows a flow diagram of an exemplary method for a RAN node (e.g., base station, eNB, gNB, DU, etc.), according to various embodiments of the present disclosure.

[0061] Figure 12 shows a communication system according to various embodiments of the present disclosure.

[0062] Figure 13 shows a UE according to various embodiments of the present disclosure.

[0063] Figure 14 shows a network node according to various embodiments of the present disclosure.

[0064] Figure 15 is a block diagram of a virtualization environment in which functions implemented by some embodiments of the present disclosure may be virtualized.

[0065] DETAILED DESCRIPTION

[0066] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided as examples to convey the scope of the subject matter to those skilled in the art.

[0067] In general, all terms used herein are to be interpreted according to their ordinary meaning to a person of ordinary skill in the relevant technical field, unless a different meaning is expressly defined and / or implied from the context of use. All references to a / an / the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise or clearly implied from the context of use. The operations of any methods and / or procedures disclosed herein do not have to be performed in the exact order disclosed, unless an operation is explicitly described as following or preceding another operation and / or where it is implicit that an operation must follow or precede another operation. Any feature of any embodiment disclosed herein can apply to any other disclosed embodiment, as appropriate. Likewise, any advantage of any embodiment described herein can apply to any other disclosed embodiment, as appropriate.

[0068] Furthermore, the following terms are used throughout the description given below:

[0069] • Radio Access Node: As used herein, a “radio access node” (or equivalently “radio network node,” “radio access network node,” or “RAN node”) can be any node in a radio access network (RAN) that operates to wirelessly transmit and / or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., gNB in a 3GPP 5G / NR network or an enhanced or eNB in a 3GPP LTE network), base station distributed components (e.g., CU and DU), a high-power or macro base station, a low-power base station (e.g., micro, pico, femto, or home base station, or the like), an integrated access backhaul (IAB) node, a transmission point (TP), a transmission reception point (TRP), a remote radio unit (RRU or RRH), and a relay node.

[0070] • Core Network Node: As used herein, a “core network node” is any type of node in a core network. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a serving gateway (SGW), a PDN Gateway (P-GW), a Policy and Charging Rules Function (PCRF), an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), a Charging Function (CHF), a Policy Control Function (PCF), an Authentication Server Function (AUSF), a location management function (LMF), or the like.

[0071] • Wireless Device: As used herein, a “wireless device” (or “WD” for short) is any type of device that is capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other wireless devices. Communicating wirelessly can involve transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information through air. Unless otherwise noted, the term “wireless device” is used interchangeably herein with the term “user equipment” (or “UE” for short), with both of these terms having a different meaning than the term “network node”.

[0072] • Radio Node: As used herein, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

[0073] • Network Node: As used herein, a “network node” is any node that is either part of the radio access network (e.g., a radio access node or equivalent term) or of the core network (e.g., a core network node discussed above) of a cellular communications network. Functionally, a network node is equipment capable, configured, arranged, and / or operable to communicate directly or indirectly with a wireless device and / or with other network nodes or equipment in the cellular communications network, to enable and / or provide wireless access to the wireless device, and / or to perform other functions (e.g., administration) in the cellular communications network.

[0074] • Node: As used herein, the term “node” (without prefix) can be any type of node that can in or with a wireless network (including RAN and / or core network), including a radio access node (or equivalent term), core network node, or wireless device. However, the term “node” may be limited to a particular type (e.g., radio access node, IAB node) based on its specific characteristics in any given context.

[0075] The above definitions are not meant to be exclusive. In other words, various ones of the above terms may be explained and / or described elsewhere in the present disclosure using the same or similar terminology. Nevertheless, to the extent that such other explanations and / or descriptions conflict with the above definitions, the above definitions should control.

[0076] Note that the description given herein focuses on a 3 GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system and can be applied to any communication system that may benefit from them.

[0077] Figure 2 shows exemplary 5G user plane (UP) and control plane (CP) protocol layers between a UE (210), a gNB (220), and an AMF (230). Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Convergence Protocol (PDCP) layers between UE and gNB are common to UP and CP. PDCP provides ciphering / deciphering, integrity protection, sequence numbering, reordering, and duplicate detection for both CP and UP, as well as header compression and retransmission for UP data.

[0078] On the UP side, Internet protocol (IP) packets arrive to PDCP as service data units (SDUs), and PDCP creates protocol data units (PDUs) to deliver to RLC. The Service Data Adaptation Protocol (SDAP) layer handles quality-of-service (QoS) including mapping between QoS flows and Data Radio Bearers (DRBs) and marking QoS flow identifiers (QFI) in UL and DL packets. RLC transfers PDCP PDUs to MAC through logical channels (LCH). RLC provides error detection / correction, concatenation, segmentation / reassembly, sequence numbering, reordering of data transferred to / from the upper layers. MAC provides mapping between LCHs and PHY transport channels, LCH prioritization, multiplexing into or demultiplexing from transport blocks (TBs), hybrid ARQ (HARQ) error correction, and dynamic scheduling (in gNB). PHY provides transport channel services to MAC and handles transfer over the NR radio interface, e.g., via modulation, coding, antenna mapping, and beam forming.

[0079] On the CP side, the non-access stratum (NAS) layer between UE and AMF handles UE / gNB authentication, mobility management, and security control. RRC sits below NAS in the UE but terminates in the gNB rather than the AMF. RRC controls communications between UE and gNB at the radio interface as well as the mobility of a UE between cells in the NG-RAN. RRC also broadcasts system information (SI) and performs establishment, configuration, maintenance, and release of DRBs and Signaling Radio Bearers (SRBs) and used by UEs. Additionally, RRC controls addition, modification, and release of carrier aggregation (CA) and dual -connectivity (DC) configurations for UEs, and performs various security functions such as key management.

[0080] After a UE is powered ON it will be in the RRC IDLE state until an RRC connection is established with the network, at which time the UE will transition to RRC CONNECTED state (e.g., where data transfer can occur). The UE returns to RRC IDLE after the connection with the network is released. In RRC IDLE state, the UE’s radio is active on a discontinuous reception (DRX) schedule configured by upper layers. During DRX active periods (also referred to as “DRX On durations”), an RRC IDLE UE receives SI broadcast in the cell where the UE is camping, performs measurements of neighbor cells to support cell reselection, and monitors a paging channel on PDCCH for pages from 5GC via gNB. An NR UE in RRC IDLE state is not known to the gNB serving the cell where the UE is camping. However, NR RRC includes an RRC_INACTIVE state in which a UE is known (e.g., via UE context) by the serving gNB. RRC INACTIVE has some properties similar to a “suspended” condition used in LTE.

[0081] As briefly mentioned above, two DL RS have a QCL relation when the respective antenna ports on which they are transmitted are configured such that the large-scale properties of a channel over which the RS on one antenna port is conveyed can be inferred from the channel over which a RS on the other antenna port is conveyed. Such large-scale properties may include one or more of delay spread, Doppler spread, Doppler shift, average gain, average delay, and spatial Rx parameters. Since the channel is estimated using a RS, two RS may also be referred to as QCL or having a QCL relation.

[0082] The RAN can indicate to a UE that two antenna ports are QCL with respect to a certain parameter. Subsequently, the UE can estimate that parameter based on one of the antenna ports and use that estimate when receiving the other antenna port. In NR, four types of QCL relations between a source RS and target RS may be indicated by a RAN node:

[0083] • Type A: {Doppler shift, Doppler spread, average delay, delay spread}

[0084] • Type B: {Doppler shift, Doppler spread}

[0085] • Type C: {average delay, Doppler shift} • Type D: {Spatial Rx parameter}

[0086] QCL type D was introduced to facilitate beam management with analog beamforming and is also known as “spatial QCL”.

[0087] In 5G, a RAN node can configure a UE (e.g., via RRC) with multiple transmission configuration indicator (TCI) states, with each TCI state providing QCL information that the UE can use to receive a target RS. In particular, the TCI state may define a QCL source RS, such that the TCI state itself may be referred to as a QCL source. Figure 3 shows an ASN. l data structure for an exemplary RRC TCI-State information element (IE).

[0088] Once configured, a TCI state can be activated by the RAN node sending the UE a TCI state activation MAC CE. Figure 4 shows an exemplary TCI state activation MAC CE, which is arranged into N octets (i.e., bytes), with N being the number of TCI states being activated. Each activated TCI state is identified by a TCI state ID, which identifies a TCI state previously configured via RRC. The Serving Cell ID field indicates the serving cell for which the MAC CE applies. If the indicated Serving Cell is configured as part of a simultaneous TCI update list, then this MAC CE applies to all serving cells in the list. This may be referred to as “unified TCI state activation.”

[0089] 3 GPP Rel-10 introduced support for channel bandwidths larger than 20 MHz in Fourthgeneration (4G) Long-Term Evolution (LTE) networks. To remain compatible with UEs from earlier releases (e.g., LTE Rel-8), a wideband LTE Rel-10 carrier appears as multiple component carriers (CCs), each having the same structure as an LTE Rel-8 carrier. A Rel-10 UE can receive the multiple CCs based on Carrier Aggregation (CA). The CCs can also be considered “cells,” such that a UE in CA has one primary cell (PCell) and one or more secondary cells (SCells) that are referred to collectively as a “cell group.”

[0090] LTE Rel-12 introduced dual connectivity (DC) whereby a UE can be connected to two network nodes simultaneously, thereby improving connection robustness and / or capacity. 5G / NR also supports various DC (or more generally, multi-connectivity) configurations for UEs. 3 GPP TR 38.804 (vl4.0.0) describes various exemplary DC scenarios or configurations in which the MN and SN can apply NR, LTE, or both. In particular, a UE is configured with a Master Cell Group (MCG) provided by a master node (MN) and a Secondary Cell Group (SCG) provided by a secondary node (SN). Each cell group includes one MAC entity, a set of logical channels with associated RLC entities, a primary cell (i.e., PCell for MCG, PSCell for SCG), and optionally one or more SCells.

[0091] Seamless mobility is a key feature of 3GPP radio access technologies (RATs). When the UE moves between the coverage areas of two cells, a serving cell change needs to be performed at some point. Currently, serving cell change is triggered by L3 (e.g., RSRP) measurements and involves RRC signaling to change PCell and PSCell (e.g., when dual connectivity is configured), as well as release / add SCells (e.g., when CA is configured).

[0092] In general, a RAN (e.g., NG-RAN) configures a UE in RRC_CONNECTED state to perform and report radio resource management (RRM) measurements to assist network- controlled mobility decisions, such as for handover from a serving cell to a target cell (e.g., PCell change). Upon the reported measurements meeting a certain condition or threshold, the serving RAN node may send a handover command to the UE, indicating a target cell for the handover. In NR, the handover command is an RRCReconfiguration message with a reconfigurationWithSync field. The procedure to perform a handover is sometimes also referred to as “L3 mobility”, as it is controlled by L3 and the RRC messages exchanged are part of L3.

[0093] These reconfigurations are prepared in advance by a target RAN node serving the target cell, upon a request from the UE’s serving RAN node. This request is transmitted over the Xn interface in case the serving and target RAN nodes are part of the NG-RAN. The reconfiguration in the handover command is based on the UE’s existing RRC configuration in its current serving cell (also referred to as “source cell”), which is indicated in the inter-node request. In some cases, the reconfiguration can be provided as a “delta” to the UE’s existing configuration in the source cell, which reduces the size of the handover command.

[0094] The reconfiguration provided by the target RAN node contains all information the UE needs to access the target cell, e.g., random access configuration, a new cell radio network temporary identifier (C-RNTI) assigned to the UE in the target cell, and parameters enabling the UE to calculate security keys that it can use when communicating with the target cell (including sending a handover complete message).

[0095] In general, UE nobility in RRC CONNECTED state is network-based since the network has the most information about conditions such as cell loading (UEs and / or traffic), available node resources (e.g., processing), available frequencies, etc. Seamless handovers ensure that the UE moves around in the coverage area of different cells without excessive interruption to data transmission. However, there will be scenarios when the network fails to handover the UE to the “correct” neighbor cell in time, which can cause the UE will declare radio link failure (RLF) or handover failure (HOF).

[0096] To address various difficulties with handovers and other mobility procedures, 3 GPP Rel- 16 includes support for conditional handover (CHO) and SN-initiated intra-SN conditional PSCell change (CPC) procedures while Rel-17 includes support for various other conditional mobility procedures. A main principle of conditional mobility is separation of transmission and execution of a mobility (e.g., handover) command. This allows the mobility command to be sent earlier to UE when the radio conditions are still good, thus increasing the likelihood that it is successfully transferred. The execution of the mobility command is done at later point in time based on an associated execution condition.

[0097] Conditional mobility procedures are based on a conditional reconfiguration framework in which the network provides a UE with one or more reconfigurations, each with associated execution condition(s). Each reconfiguration can be provided in an RRCReconfiguration message (in NR) or an RRCConnectionReconfiguration message (in LTE). When the UE later detects the execution condition(s) associated with one of the earlier-received reconfigurations, the UE executes the associated reconfiguration to perform the mobility procedure (e.g., HO, PSCell change, PSCell addition, etc.).

[0098] Even so, conditional (e.g., CHO) and non-conditional (e.g., HO) are triggered by layer 3 (L3) measurements and involves radio resource control (RRC) signaling to change PCell and PSCell (e.g., when DC is configured), as well as release / add SCells as needed. Moreover, conventional inter-cell mobility involves complete layer 2 (L2) and layer 1 (LI, i.e., PHY) resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching.

[0099] 3GPP Rel-18 includes new mobility procedures that facilitate serving cell changes via L1 / L2 signaling to address these problems and / or difficulties. These new procedures are often referred to as L1 / L2 based inter-cell mobility or L1 / L2 triggered mobility (LTM). In LTM, a UE is pre-configured by its serving RAN node with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration.” The UE performs measurements on configured LTM candidate cells and transmits corresponding measurement reports to the RAN node, based on which the RAN node triggers execution of a LTM cell switch procedure by the UE to one of the configured LTM candidate cells. The RAN node may trigger the LTM cell switch procedure by sending the UE an LTM cell switch command.

[0100] In LTM, a UE is pre-configured by its serving RAN with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration.” This RRC configuration may be an RRCReconfiguration message or a portion thereof, such as one or more lEs / fields / parameters (e.g., CellGroupConfig IE). The UE performs measurements on configured LTM candidate cells and transmits corresponding measurement reports to the RAN, which triggers the execution of a LTM cell switch procedure by the UE to one of the configured LTM candidate cells. This triggering is done by transmitting an LTM cell switch command to the UE in lower layer signaling (e.g., DCI or MAC CE). Based on this command, the UE connects to the associated LTM candidate cell and uses the previously received RRC configuration for this cell.

[0101] Regarding terminology, a candidate cell configured for a UE mobility procedure (e.g., LTM or L3) becomes a target cell when the UE performs the mobility procedure, either due to a command from the UE’s current serving RAN node or due to execution conditions being met at the UE. As such, in the context of conditions. As such, the terms “candidate,” “target,” and “candidate (target)” may be used interchangeably when referring to that cell or to the RAN node serving that cell. Likewise, the UE’s serving cell becomes when the UE performs the mobility procedure, and so the terms “source,” “serving,” and “serving (source)” may be used interchangeably when referring to that cell or to the RAN node serving that cell.

[0102] Figure 5 shows a signaling diagram for an exemplary LTM cell switch procedure. Although the operations are shown with numerical labels, this is done to facilitate explanation rather than to require or imply any specific operational order, unless expressly stated otherwise.

[0103] In operation 1, the UE (510) sends MeasurementReport message to the gNB (520). Based on this message, the gNB decides to configure LTM for the UE and initiates preparation of one or more LTM candidate cells. In operation 2, the gNB sends an RRCReconfiguration message to the UE including LTM candidate cell configurations of one or more candidate cells. In operation 3, the UE stores the received LTM candidate cell configurations and transmits an RRCReconfigurationComplete message to the gNB.

[0104] Since a goal of LTM is to reduce interruption time for UE data transmissions, the UE needs to be ready to communicate with an LTM candidate cell upon (or shortly after) receiving the L1 / L2 signaling for mobility execution from the source cell. For example, the UE must be able to transmit UL data or a scheduling request (SR) to the LTM candidate cell and / or monitor a DL control channel (e.g., PDCCH) from the LTM candidate cell. In other words, UE needs to know the cell that it is moving to so it can apply the corresponding configuration, including the correct timing alignment and / or TCI state for the cell. Likewise, in the case of inter-DU LTM, when the source DU transmits the L1 / L2 signaling for mobility execution, the target DU needs to be prepared for scheduling UL and DL transmissions for the UE in the target cell, and for receiving SR from the UE.

[0105] The UE performs operations 4a-b before receiving any LTM cell switch command. In operation 4a, the UE performs early DL synchronization with the configured LTM candidate cells. Each LTM candidate cell configuration may include a configuration for early DL synchronization, which may also be referred to as an “LTM candidate TCI state configuration” or more simply as a “TCI state configuration.” For example, the TCI state configuration may include an RRC CandidateXcI -State IE and / or an RRC CandidateXcI-Ul -State IE. Figure 6 shows an exemplary CandidateXcI -State IE. Figure 7 shows an exemplary CandidateXcI -UL -State IE.

[0106] Each TCI state for an LTM candidate may be a DL TCI state, an UL TCI state, or a joint DL / UL TCI state. Each DL or joint TCI state may have one or two QCL types, each of which is associated with a DL RS. This may be configured using the exemplary ('andidatQ[d-State IE shown in Figure 6. Each UL TCI state is associated with one or more DL RS, which may be configured by the exemplary CandidateXcI-Ul .-State IE shown in Figure 7. Each of these IES includes a field that assigns an identifier to the configured TCI state.

[0107] Figure 8 shows an exemplary RRC LTM-Candidate IE, which can be used to provide an LTM candidate cell configuration to a UE. The LTM-Candidate IE includes an Itm-DL- OrJointTCI-StateToAddModList field, which is a sequence of CandidateXcI -State IEs - one for each DL or joint UL / DL TCI state to be configured for the LTM candidate cell. The LTM- Candidate IE also includes an Itm-UL-TCI-StateToAddModList field, which is a sequence of CandidateXcI-UL-State IEs - one for each UL TCI state to be configured for the LTM candidate cell. The LTM-Candidateld field identifies the particular LTM candidate cell.

[0108] Once configured in this manner, early TCI state activation in an LTM candidate cell may be triggered by a MAC CE from the serving RAN node. Figure 9 shows an exemplary LTM candidate cell TCI state activation / deactivation MAC CE. The Candidate Cell ID field in octet 1 carries an ID of the LTM candidate cell for which N > 1 TCI states are to be activated. The remaining “R” bits in octet 1 are reserved.

[0109] The N TCI state ID fields indicates identify the respective TCI states to be activated for the indicated LTM candidate cell. These TCI state IDs correspond to TCI state IDs previously configured via RRC, such as via Itm-DL-OrJointTCI-StateToAddModList or Itm-UL-TCI- StatesToAddModList field. The D / U field in each octet indicates whether the TCI state ID in the same octet is for a joint / DL TCI state (value 1) or for an UL TCI state (value 0).

[0110] Each “Pi” field indicates whether the ith TCI state ID field identifies multiple TCI states or a single TCI state. If Pi = 1, the i-th TCI codepoint TCI state ID field identifies the DL TCI state and the UL TCI state. If Pi = 0, the i-th TCI codepoint TCI state ID field identifies only a DL / joint TCI state or only an UL TCI state, according to the corresponding D / U bit.

[0111] Returning to Figure 5 operation 4b, when UE-based TA measurement is configured, UE acquires the TA value(s) of the candidate cell(s) by measurement. Otherwise, in operation 4b, the UE performs early TA acquisition with the candidate cell(s) as requested by the network. This is done via contention-free random access (CFRA) triggered by a physical DL control channel (PDCCH) order from the source cell, following which the UE sends a RA preamble towards the indicated LTM candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the LTM candidate cell(s), the UE doesn’t receive RA response (with TA) from the LTM candidate cell; instead, TA for the LTM candidate cell is indicated in a subsequent LTM cell switch command. Similarly, the UE doesn’t maintain a TA timer for the LTM candidate cell but relies on the RAN to guarantee the TA validity. In operation 5, the UE performs LI measurements on the configured LTM candidate cells and transmits LI measurement reports to the gNB. The UE performs such LI measurement as long as the LTM candidate cell configurations received in operation 2 remain applicable.

[0112] In operation 6, the gNB decides to trigger an LTM cell switch for the UE to one of the configured LTM candidate cells ( “target cell”) and transmits an LTM cell switch command, which is a MAC CE that includes an identifier (e.g., index) of the corresponding LTM candidate cell configurations provided to the UE in operation 2. The MAC CE may also include an identifier of a beam (e.g., a TCI State ID) by which the UE should access the target cell.

[0113] The gNB selects the identified beam based on the LI measurements reported by the UE. These are typically per-beam measurements, such as LI reference signal received power (RSRP) for synchronization signal / PBCH blocks (SSBs). These measurements may not be layer 3 (L3) filtered, so they may change relatively frequently as UE radio conditions change. As such, it may be challenging for the gNB to determine the optimal beam to indicate to the UE in the LTM cell switch command.

[0114] Upon receiving the LTM cell switch command, the UE monitors PDCCH on the indicated beam of the target cell. In other words, the UE considers the TCI state for the indicated beam / TCI state ID to be “activated” when performing the LTM cell switch. The UE also applies the configuration identified in the MAC CE.

[0115] In operation 7, if UE does not have valid TA of the target cell, the UE performs a RA procedure towards the target cell,. The UE performs CFRA if the LTM cell switch command contains the necessary information, as specified in clause 6.1.3.xy of 3GPP TS 38.321 (vl7.7.0). In operation 8, the UE completes the LTM cell switch procedure by sending RRCReconfigurationComplete message to the gNB via the target cell. If the UE has performed a RA procedure in operation 7, the UE considers that LTM cell switch execution is successfully completed when the RA procedure is successfully completed. For RACH-less LTM, the UE considers that LTM cell switch execution is successfully completed when the UE determines that the gNB has successfully received its first UL data. The UE determines successful reception of its first UL data by receiving a PDCCH addressing the UE’s C-RNTI in the target cell, which schedules a new transmission following the first UL data. The PDCCH carries either a DL assignment or an UL grant addressing the same HARQ process as the first UL data.

[0116] The split CU / DU architecture shown in Figure 1 also supports LTM, including for intra- DU and inter-DU / intra-CU cell changes. In the inter-DU / intra-CU scenario, the candidate cell for LTM is a cell served by a neighbor DU to the source DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). In the intra-DU scenario, the candidate cell for LTM is a cell served by the same DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). Since the procedure shown in Figure 8 involves a single gNB, it can also be considered an intra-CU LTM cell switch.

[0117] In contrast, an inter-CU (or inter-gNB) LTM procedure involves a cell switch from a source cell served by a first CU / gNB to a candidate (target) cell served by a second CU / gNB. In addition to the operations described above in relation to Figure 5, UE actions performed during an inter-CU LTM cell switch procedure may also include other actions such as refresh of security keys. As such, an inter-CU LTM configuration may include the same information as an intra-CU LTM configuration as well as one or more of the following:

[0118] • Information needed to perform security key refresh, e.g., MasterKeyUpdate IE or a RadioBearerConfig IE that includes SecurityConfig with SecurityAlgorithmConfig

[0119] • Indication to perform L2 / PDCP re-establishment; and

[0120] • Indication to perform a full configuration, e.g., RRC field fullConfig.

[0121] As mentioned above, there are some notable differences between Rel-18 LTM and conditional L3 mobility. For example, unlike conditional L3 mobility in which the UE initiates execution, LTM is initiated by a UE’s serving RAN node based on measurements reported by the UE. This introduces some amount of delay in an LTM cell switch. To capture advantages of both LTM and conditional L3 mobility, 3GPP Rel-19 will introduce conditional LTM (CLTM). Much like conditional L3 mobility, a UE is configured with CLTM execution conditions along with the LTM candidate cell configurations. When a UE detects CLTM execution condition(s) associated with an earlier-received LTM candidate cell configuration, the UE executes an LTM cell switch to the candidate cell.

[0122] The UE’s evaluation of a CLTM execution condition associated with an LTM candidate cell is based on lower layer measurements, such as LI reference signal received power (Ll-RSRP) and / or SS-RSRP, derived from SSBs and / or CSLRSs of the UE’s source cell and / or the LTM candidate cell. Lower layer measurements include measurements reported to support lower layer procedures like beam management, candidate cell TCI state activation / deactivation, early TA acquisition, link adaptation, etc. Unlike L3 measurements, lower layer measurements are not filtered based on L3 parameters, although some filtering may be performed based on the other lower layer parameters.

[0123] A CLTM execution condition may include an indication of the condition and / or a configuration such as event identifier(s), offset(s), threshold(s), RS type, trigger quantity (e.g., RSRP, RSRQ, SINR, etc.), time-to-trigger (TTT), etc. A CLTM execution condition may also be referred to as LTM execution condition, triggering condition, or a similar term.

[0124] For CLTM, typically a UE evaluates one or two CLTM execution conditions and performs a LTM cell switch when the CLTM execution condition(s) is / are fulfilled, without reception of an explicit LTM cell switch command from the RAN. In other words, upon satisfaction of the CLTM execution condition(s), the UE initiates an LTM cell switch.

[0125] In both LTM and CLTM, multiple LTM candidate cells configured for a UE may have similar UL synchronization characteristic and / or belong to the same “UL synchronization group” that is associated with some group identity (e.g., UL sync group ID). In such case, the UE may have an identical (or single) TA value for these multiple LTM candidate cells, and the same Time alignment timer (TAT) is applicable in case the UE executes LTM cell switch to any of those LTM candidate cells. This relationship may also be modelled as Timing Advance Group (TAG), which is defined as an RRC-configured group of serving cells that use the same timing reference cell and the same TA value (when UL is configured). In some cases, the UL synchronization group and / or TAG relationship may be due to the multiple LTM candidate cells being provided by a single DU, which may be the UE’s serving DU (S-DU) or another DU (e.g., candidate DU, C- DU).

[0126] Currently, 3 GPP RAN2 working group has made various agreements regarding CLTM standardization, including the following:

[0127] • Source cell sends the conditional LTM configuration via RRCReconfiguration to UE, which includes the LTM candidate configurations, and the corresponding execution conditions.

[0128] • Event LTM3-like and LTM5-like are used as the conditional LTM execution condition. FFS on reuse of CHO conditions.

[0129] • Source cell and each candidate cell provides its own execution condition for conditional LTM.

[0130] • DU generates the LI execution condition. FFS on a case that L3 measurement is used.

[0131] • RACH-less conditional intra-CU LTM is supported.

[0132] • RACH based conditional intra-CU LTM is supported.

[0133] • UE based TA measurement mechanism is supported for conditional intra-CU LTM.

[0134] • PDCCH ordered early TA acquisition is supported for conditional LTM.

[0135] • Rel-18 Early candidate TCI State activation / deactivation is supported for conditional intra-CU LTM.

[0136] • For RACH-less conditional LTM, CG-based first UL transmission on target cell is supported. FFS on DG-based approach.

[0137] • The LTM completion defined for Rel-18 intra-CU LTM is reused for conditional LTM.

[0138] In both LTM and CLTM, the UE needs to receive two messages for early UL / DL synchronization: a TCI state activation MAC CE (for DL) and a PDCCH order (for UL). Even so, the same beam (e.g., SSB index) in an LTM candidate cell is often associated with both TA acquisition and TCI activation procedure, e.g., for joint UL and DL TCI states. As such, sending the UE two messages about the same beam wastes scarce signaling resources. In addition, it is often quite critical to perform both UL / DL synchronization procedures before LTM execution due to reception of an LTM cell switch command or fulfillment of CLTM execution conditions.

[0139] Moreover, in some cases the same UE processing needs to be performed for both the TCI state activation MAC CE and the PDCCH order. LI measurement adds significant complexity and signaling overhead to the system and LI measurement reports require additional resources, which may negatively impact the network capacity and the overall user experience. Although 3 GPP specifications indicate UE LI measurements are optional, when the UE does not perform LI measurements, the duration required by the UE between reception of the PDCCH order for early UL synchronization and transmission of the RA preamble includes the time to acquire and process the corresponding DL SSB, even though the UE has already been ordered to perform early DL downlink synchronization that also involves acquiring and processing the DL SSB. This adds an unnecessary and undesirable delay.

[0140] Accordingly, embodiments of the present disclosure address these and related problems and / or issues by various techniques in which a UE is provided (e.g., by a serving RAN node) a single command to perform TA acquisition (or early UL synchronization) and TCI state activation (or early DL synchronization) for an LTM candidate cell. The single command may include an identifier of the LTM candidate cell for which the UE should perform such actions.

[0141] In some embodiments, the single command may include a RS (or beam) identifier, such as an SSB index. In such embodiments, the UE performs TA acquisition by selecting a RA preamble and / or other resources associated with the RS identifier and transmits toward the LTM candidate cell using the selected RA preamble / resources. Additionally, the UE activates the candidate TCI state of the LTM candidate cell having as its QCL source (e.g., type D) the RS (e.g., SSB) identified by the RS identifier.

[0142] In other embodiments, the single command may include a candidate TCI state ID, which identifies a TCI state for the LTM candidate cell. The TCI state may include a QCL source RS identified by a RS identifier (e.g., SSB index). In such embodiments, the UE performs TA acquisition by selecting a RA preamble and / or other resources associated with the QCL source RS identifier associated with the received candidate TCI state ID, and transmits toward the LTM candidate cell using the selected RA preamble / resources. Additionally, the UE activates the candidate TCI state of the LTM candidate cell that is identified by the candidate TCI state ID received in the single command. Embodiments of the present disclosure may provide various advantages and / or benefits. For example, by providing a single command that triggers early UL and early DL synchronization, embodiments may reduce L1 / L2 signaling overhead associated with LTM / CLTM procedures. Moreover, by providing such a single command, embodiments may facilitate more timely UE LTM execution by reducing and / or eliminating duplicative operations (e.g., SSB processing) needed for both early UL and early DL synchronization. In other words, the UE may perform a single operation in response to a single command, thereby reducing and / or eliminating the delay associated with duplicative operations responsive to multiple commands. At a high level, embodiments may facilitate mobility without connection interruption, excess signaling overhead, and excess UE energy consumption.

[0143] In the present disclosure, the following terms may be used interchangeably: “L1 / L2 based inter-cell mobility”, “L1 / L2 mobility,” “LI -mobility,” “LI based mobility,” “Ll / L2-centric inter-cell mobility,” “L1 / L2 inter-cell mobility,” “inter-cell beam management,” “inter-DU L1 / L2 based inter-cell mobility”, and “L1 / L2 triggered mobility” (or LTM). These terms refer to a scenario in which a UE receives lower layer (i.e., below RRC, such as MAC or PHY) signaling from a network indicating for the UE to change of its serving cell (e.g., PCell) from a source cell to a target cell.

[0144] The content of the lower layer signaling may be referred to as “LTM cell switch command”. Exemplary lower layer signaling includes LI DL control information (DCI) and L2 MAC control element (CE). Compared to conventional RRC signaling, lower layer signaling reduces processing time and interruption time during mobility and may also increase mobility robustness since the network can respond more quickly to changes in the UE’s channel conditions.

[0145] The term “LTM candidate cell” refers to a cell for which the UE is configured for LTM, specifically a cell the UE can move to in a LTM cell switch procedure in response to receiving an LTM cell switch command. An LTM candidate cell may also be referred to herein as “candidate cell”, “(LTM) candidate, “mobility candidate”, “non-serving cell”, “additional cell”, “(LTM) target candidate cell”, “(LTM) target candidate”, and comparable terms. A UE may perform and report measurements (e.g., CSI measurements) on an LTM candidate cell, based on which the UE’s serving RAN node may make an informed decision about which beam (or TCI state) and / or cell to switch the UE. An LTM candidate cell may be a candidate to be a target PCell or PSCell, or an SCell of a cell group (e.g., MCG SCell). In the case of LTM fast recovery, when a failure is detected and the UE selects an LTM candidate cell, the UE performs an LTM cell switch towards the selected LTM candidate cell (e.g., by applying the associated LTM candidate cell configuration) rather than performing RRC re-establishment. The change of serving cell (e.g., PCell) may also lead to a change in SCell(s) of the same cell group, e.g., in case an LTM cell switch command triggers the UE to change to another cell group configuration of the same type (e.g., another MCG configuration). For example, an LTM cell switch may include a change in SpCell (e.g., PCell for MCG, PSCell for SCG) and a change (e.g., addition, modification and / or release) in SCells of the same cell group. This may happen when the command triggers the UE to change to another cell group configuration of the same type (e.g., another SCG configuration).

[0146] Before the UE receives the LTM cell switch command, the UE is configured by the network with one or more “LTM candidate cell configurations” via an RRCReconfiguration message. The terms “(LTM) candidate configuration”, “(LTM) candidate target cell configuration”, and “(LTM) target candidate (cell) configuration” may be used interchangeably with LTM candidate cell configuration.

[0147] An LTM candidate cell configuration may be included in an RRC IE such as CellGroupConfig, SpCellConfig, or SCellConfig and / or an embedded RRCReconfiguration message for an LTM candidate cell. An LTM candidate cell configuration includes configuration parameters the UE needs to operate in that LTM candidate cell when it performs an LTM cell switch procedure, e.g., upon reception of the LTM cell switch command. As some more specific examples, an LTM candidate cell configuration can include a PCell configuration and one or more SCell configurations of an MCG, or a PSCell configuration and one or more SCell configurations of an SCG. The exact content and / or structure of the IE and / or embedded message for an LTM candidate cell configuration may be called “RRC model for the candidate configuration” or more simply “RRC model”.

[0148] A UE may receive an LTM candidate cell configuration in complete form or as a delta (or difference) relative to a reference configuration (which may be signaled separately). In the latter case, the actual LTM candidate configuration is a combination of the delta configuration and the reference configuration.

[0149] The lower layer signaling from the RAN may include an identifier (or index) associated with an LTM candidate cell configuration. The identifier may be sent together with an LTM cell switch command, indicating for the UE to perform an LTM cell switch to the associated LTM candidate cell.

[0150] The term “LTM configuration” refers to a data structure that is used for or related to UE LTM operations, and may include one or more of the following elements (non-exclusive):

[0151] • an LTM candidate cell configuration, such as one or more of the following for an LTM candidate cell: o lower layer information, such as Ll / PHY configuration, L2 / MAC / RLC configuration, cell group configuration, serving cell configuration, etc.; and o higher layer information, such as L3 / RRC parameter and / or timer values, PDCP configuration, radio bearer configuration, L3 / RRC measurement configuration, etc.;

[0152] • a measurement configuration, e.g., measurements for LTM, measurement reports for LTM, CSI resource configuration for LTM, CSI report configuration for LTM, etc.;

[0153] • a configuration for early DL synchronization, e.g., for early TCI state activation;

[0154] • a configuration for early UL synchronization, e.g., for transmission of PDCCH ordered preamble transmission and reception of timing advance (TA);

[0155] • a configuration for execution of an LTM cell switch procedure according to a given LTM candidate cell configuration (e.g., whether to perform RA, RLC reestablishment, MAC reset, PDCP recovery, etc.).;

[0156] • additional information needed for an intra-CU / gNB LTM cell switch procedure.

[0157] The term “part of an LTM configuration” may refer to a subset of the elements in the above list, and / or a subset of items comprising any of the elements present (e.g., subset of configurations for DL pre-sync).

[0158] The phrase “LTM cell switch procedure” refers to the process of a UE switching (or changing) from a source cell to a target cell (i.e., an LTM candidate cell) using LTM. An LTM cell switch procedure may also be referred to as “L1 / L2 based inter-cell mobility execution”, “LTM execution”, “dynamic switch”, “LTM switch”, “(LTM) cell switch”, “(LTM) serving cell change”, or “(LTM) cell change”. Similarly, the phrase “switching to an LTM candidate cell configuration” means that the UE applies an LTM candidate cell configuration such that the associated LTM candidate cell becomes its new special cell (SpCell, e.g., PCell for LTM in MCG or PSCell for LTM in SCG) or its new SCell. In other words, an LTM candidate cell can be a candidate for the UE’s PCell, PSCell, or SCell.

[0159] Furthermore, an LTM cell switch may involve a UE switching (or changing) from a source cell group to a target cell group using LTM. For example, this may involve a change in the SpCell for a cell group (e.g., PCell for MCG, PSCell for SCG), a change in SCells of the cell group (e.g., addition, modification, and / or release of one or more SCells), and / or a swap between SpCell and SCell roles for two cells in the same cell group. More generally, embodiments are not limited to cells but are applicable to any UE switch from a first (or source) set of radio resources to a second (or target) set of radio resources.

[0160] Embodiments will now be described in more detail. In some embodiments, a UE configured with at least one LTM candidate cell receives (e.g., from the UE’s serving RAN node) a single command (e.g., PDCCH order, MAC CE, RRC message, a single L3 protocol message, a single L2 protocol message, a single LI protocol message, etc.) to perform TA acquisition (or early UL synchronization) and TCI state activation (or early DL synchronization) for an LTM candidate cell. The single command may include an identifier of the LTM candidate cell for which the UE should perform such actions. In some embodiments, the single command may also include one or more of the following:

[0161] • a RS (or beam) identifier, such as an SSB index associated with the LTM candidate cell; and

[0162] • an identifier of a TAG associated with the identified beam / RS.

[0163] In such embodiments, the UE performs TA acquisition by selecting a RA preamble and / or other resources associated with the RS identifier and transmits toward the LTM candidate cell using the selected RA preamble / resources. Additionally, the UE activates the candidate TCI state which has as QCL source (e.g., type D) the RS (e.g., SSB) identified by the RS identifier.

[0164] In other words, a single command triggers the UE to perform TA acquisition procedure and TCI state activation for the LTM candidate cell. As a more specific example, a single PDCCH order triggers the UE to perform early UL and DL synchronization to the LTM candidate cell, which may later become a target cell for an LTM cell switch. In some of these embodiments, the UE receives the single command after receiving an RRCReconfiguration message that includes an LTM configuration, a CLTM configuration, and / or a unified mobility configuration for both LTM and CLTM.

[0165] In some embodiments, in response to the single command, the UE sends an UL message (e.g., RA preamble, SRS, UL sync sequence, etc.) on an UL resource (e.g., PRACH time / frequency resource) of the indicated LTM candidate cell, specifically an UL resource associated with the RS (or beam) and the TAG indicated in the single command. Additionally, the UE activates a TCI state of the indicated LTM candidate cell, specifically a TCI state whose configured QCL source RS matches (or corresponds to) the RS (or beam) indicated in the single command.

[0166] In some of these embodiment, the UE first activates the TCI state and then sends the UL message to the indicated LTM candidate cell. In other of these embodiment, if the TCI state whose QCL source RS matches (or corresponds to) the RS (or beam) indicated in the single command is already activated, the UE only sends the UL message to the indicated LTM candidate cell. In some of these embodiments, if the UE previously performed early TA acquisition for the indicated LTM candidate cell and the obtained TA value is still valid, the UE only activates the matching TCI state for the LTM candidate cell.

[0167] As mentioned above, the single command may be a PDCCH order. For example, the PDCCH order may have a specific format that indicates it is for combined TA acquisition and TCI state activation for the LTM candidate cell. As another example, the PDCCH order may include a field that indicates (e.g., by containing a specific value) it is for combined TA acquisition and TCI state activation for the LTM candidate cell.

[0168] As mentioned above, the single command may be a MAC CE. For example, the MAC CE include or be associated with an identifier (e.g., an assigned logical channel ID and / or a logical channel group ID) that indicates it is for combined TA acquisition and TCI state activation for the LTM candidate cell. As another example, the MAC CE may include a field that indicates (e.g., by containing a specific value) it is for combined TA acquisition and TCI state activation for the LTM candidate cell.

[0169] Alternately, the single command may be a single MAC protocol data unit (PDU) that includes two MAC CEs, one that triggers UE TA acquisition and a second that triggers UE TCI state activation. In case the RAN wants the UE to perform TA acquisition procedure and TCI state activation for an LTM candidate cell at the same time, it is has to include the two MAC CE in the same MAC PDU. In some embodiments, the MAC PDU (may also indicate which of these operations / MAC CEs should be executed first, regardless of the order in which they are received or processed by the UE. Alternately, such an indication may be sent / received in another RRC message.

[0170] As mentioned above, the single command may be an RRC message. For example, the RRC message may include an indication (e.g., field with specific value, presence of a field, etc.) that it is for combined TA acquisition and TCI state activation for the LTM candidate cell. As mentioned above, the single command may be a single LI protocol message, such as a Downlink Control Indication (DCI) message.

[0171] In some embodiments, there may be various ways how the UE determines that the single command (e.g., PDCCH order, MAC CE) triggers both TA acquisition and TCI state activation for the LTM candidate cell. Some examples are discussed below.

[0172] As one example, a field, information element (IE), or parameter in a previous message (e.g., RRC message) explicitly indicates that the UE should perform both TA acquisition and TCI state activation for the LTM candidate cell. In some variants, the field / IE / parameter may be associated with a particular LTM candidate cell, i.e., one such field per configured LTM candidate cell. As a specific example, when the field / IE / parameter is included in an RRC configuration for a first LTM candidate cell and the UE receives a PDCCH order for triggering TA acquisition for the first LTM candidate cell, the UE also activates a TCI state for the first LTM candidate cell in response to the single command. The candidate TCI state to be activated is the one associated with the indicated SSB index (or CSLRS identifier) in the PDCCH order. In this specific example, the content of the PDCCH order may be similar to the existing PDCCH order for TA acquisition, with the RRC field / IE / parameter indicating that its reception should trigger the UE to perform early UL and DL synchronization.

[0173] As another specific example, when the field / IE / parameter is included in an RRC configuration for a second LTM candidate cell and the UE receives a MAC CE for activation of an identified TCI state (e.g., included TCI state ID) for the second LTM candidate cell, the UE also performs TA acquisition in the second LTM candidate cell using RA preamble and / or PRACH resources associated with the QCL source RS (e.g., SSB) associated with the TCI state ID in the MAC CE. In other words, the RA preamble and / or PRACH resources on which the UE transmits are selected based on the SSB (or CSLRS) configured as QCL source (e.g., type ‘D’) of the indicated TCI state. In this specific example, the content of the MAC CE may be similar to existing MAC CEs for TCI state activation, with the RRC field / IE / parameter indicating that its reception should trigger the UE to perform early UL and DL synchronization.

[0174] As another example, the UE may be configured with two or more LTM candidate cells that have the same UL synchronization characteristics (e.g., part of a TAG) and may be further configured (e.g., via RRC IE such as EarlyULSyncInformation) to perform early UL and DL synchronization procedures towards all configured LTM candidate cells with the same UL synchronization characteristics (e.g., part of a TAG, served by same DU, etc.) upon reception of a single command. As a more specific example, the UE receives a PDCCH order for triggering TA acquisition for one of the LTM candidate cells of the TAG, and triggers TA acquisition based on the information provided in the PDCCH order (e.g., RA preamble associated with indicated SSB index) as well as activating a candidate TCI state for that LTM candidate cell. In addition, the UE also activates the Joint / UL TCI states in other configured LTM candidate cells of the same TAG. The TCI state to be activated in all the LTM candidate cells is associated with the SSB index (or CSLRS resource identifier) indicated in the PDCCH order.

[0175] As another example, a format of the single command indicates that the UE should perform both TA acquisition and TCI state activation for the LTM candidate cell. As a more specific example, the UE receives a PDCCH order in a specific format which indicates that the UE should also perform early DL synchronization in addition to early UL synchronization as conventional. In response to the PDCCH order in that specific format, the UE triggers both TA acquisition and TCI state activation for the LTM candidate cell indicated by the PDCCH order, particularly using the RS (or beam) indicated by the PDCCH order. In this specific example, the content of the PDCCH order may be similar to the existing PDCCH order for TA acquisition, with the difference being the new format indicating combined early UL and DL synchronization.

[0176] As another example, a field / IE / parameter in the single command explicitly indicates that the UE should perform both TA acquisition and TCI state activation for the LTM candidate cell. As a more specific example, the UE receives a MAC CE with a specific Logical Chanel (LC) ID or Logical Channel Group (LCG) ID which indicates that the UE should also perform early UL synchronization for the LTM candidate cell in addition to early DL synchronization as conventional. In response to the MAC CE with that specific LCID or LCGID, the UE triggers both TA acquisition and TCI state activation for the LTM candidate cell indicated by the MAC CE, particularly using the RS (or beam) indicated by the MAC CE. In this specific example, the content of the MAC CE may be similar to the existing MAC CE for TCI state activation, with the difference being the new LCID or LCGID indicating combined early UL and DL synchronization.

[0177] As another specific example, the MAC CE may include a field containing a value (e.g., an integer or Boolean) which indicates that the UE should also perform early UL synchronization for the LTM candidate cell in addition to early DL synchronization as conventional.

[0178] As another example, if the UE receives a MAC PDU with two MAC CEs, one for the TCI state activation in the LTM candidate cell and one for triggering TA acquisition in the LTM candidate cell, the combination of these two MAC CEs indicates that the UE should perform early UL and DL synchronization for the LTM candidate cell (e.g., at the same time or sequentially). As mentioned above, the RAN may also indicate the order in which these operations should be executed by the UE, regardless of the order in which the MAC CEs are received or processed by the UE. For example, this may be indicated in the MAC PDU, in the MAC CEs, or within a previously received RRC message.

[0179] As mentioned above, in some embodiments, a single PDCCH order triggers a UE to perform both TA acquisition and TCI state activation for an LTM candidate cell. In response to the PDCCH order, in the TA acquisition procedure, the UE selects an SSB (or a CSLRS) corresponding to the SSB index (or CSLRS resource identifier) indicated in the PDCCH order, and a PRACH time / frequency resource associated with the selected SSB (or CSLRS), and sends a RA preamble on the selected PRACH time / frequency resource. In response the UE receives a MAC CE including a TA value to be applied toward the LTM candidate cell. In addition, the UE activates the TCI state whose QCL source RS matches (or corresponds to) the SSB index indicated in the PDCCH order.

[0180] In some of these embodiments, when the UE is configured with two or more LTM candidate cells that have the same UL synchronization characteristics (e.g., part of a TAG) and receives a PDCCH order for TA acquisition for one of these LTM candidate cells, the UE triggers TA acquisition and TCI state activation for the indicated LTM candidate cell, with both procedures also being based on an SSB index indicated by the PDCCH order (as discussed above). Additionally, the UE also activates the UL / Joint TCI states in one or more of the other LTM candidate cells with the same UL synchronization characteristics (e.g., part of the TAG), which also have as the QCL source the SSB index indicated in the PDCCH order.

[0181] In other words, a single PDCCH order triggers TA acquisition for one of the LTM candidate cells with the same UL synchronization characteristics (e.g., part of the TAG) as well as activation of UL / Joint TCI states in one or more of the other LTM candidate cells with the same UL synchronization characteristics (e.g., part of the TAG). In response to the PDCCH order, the UE starts TA acquisition in the LTM candidate cell indicated by the PDCCH order by selecting an SSB corresponding to the SSB index (or CSLRS resource identifier) indicated in the PDCCH order, and selecting a PRACH time / frequency resource associated with the selected SSB (or CSL RS), on which the UE transmits a RA preamble to the LTM candidate cell. Also in response to the PDCCH order, the UE activates UL / Joint TCI states in one or more of the other LTM candidate cells with the same UL synchronization characteristics (e.g., part of the TAG), and with a QCL source RS being the indicated SSB index in the PDCCH order.

[0182] As mentioned above, in some embodiments, a single MAC CE triggers a UE to perform both TA acquisition and TCI state activation for an LTM candidate cell based on a TCI State ID indicated in the MAC CE. In response to the MAC CE, the UE activates the TCI state associated with the TCI state ID in the MAC CE, selects an SSB (or a CSLRS) corresponding to the SSB index (or CSLRS resource identifier) configured as QCL source RS (e.g., type ‘D’) of the indicated TCI state ID of the LTM candidate cell, selects a PRACH time / frequency resource associated with the selected SSB (or CSLRS), and sends a RA preamble on the selected PRACH time / frequency resource.

[0183] As mentioned above, the single command may be an RRC message. In some of these embodiments, the RRC message may be a “lean” RRC message that includes an indication of the LTM candidate cell and a TCI state ID but few (if any) other fields / IEs / parameters. Due to the limited set of fields / IEs / parameters, the UE is able perform ASN.1 decoding and validity checking of the lean RRC message more quickly than for a conventional RRC message. As such, the time between UE reception of the lean RRC message and responsive UE initiation of TA acquisition and / or TCI state activation for the LTM candidate cell is reduced relative to the case of using a conventional RRC message to trigger these UE operations toward the LTM candidate cell. In general, the UE may perform the TA acquisition and / or TCI state activation for the LTM candidate cell based on the lean RRC message content in a similar manner as discussed above for other single commands (e.g., PDCCH orders, MAC CEs) with identical content.

[0184] In other of these embodiments, when the UE is configured with two or more LTM candidate cells that have the same UL synchronization characteristics (e.g., part of a TAG) and receives a lean RRC message that includes an indication of one of these LTM candidate cells, the UE triggers TA acquisition and TCI state activation for the indicated LTM candidate cell, with both procedures also being based on an SSB index indicated by the lean RRC message (as discussed above). Additionally, the UE also activates the UL / Joint TCI states in one or more of the other LTM candidate cells with the same UL synchronization characteristics (e.g., part of the TAG), which also have as the QCL source the SSB index indicated in the lean RRC message.

[0185] In some embodiments, when the UE receives the single command (e.g., PDCCH order, MAC CE, lean RRC message, etc.), the UE starts a timer. While the timer is running, the UE needs to maintain early DL synchronization with the LTM candidate cell indicated by the single command. In other words, while the timer is running the UE may need to perform one or more measurements with a defined periodicity to monitor early DL synchronization with the LTM candidate cell and, if early DL synchronization is lost, trigger new acquisition of early DL synchronization with the LTM candidate cell. When the timer expires, the UE is no longer required to maintain early DL synchronization with the LTM candidate cell.

[0186] In some of these embodiments, the UE may stop the running timer in response to one or more of the following conditions:

[0187] • receiving an LTM cell switch command;

[0188] • triggering LTM cell switch upon fulfillment of one or more CLTM execution conditions;

[0189] • receiving a handover command (e.g., RRCReconfiguration including reconfiguration with sync IE);

[0190] • receiving an RRC message that releases the LTM or CLTM candidate cell configuration for which the timer was started; and

[0191] • receiving an RRC message that reconfigures early UL and DL synchronization of the LTM candidate cell for which the timer was started.

[0192] In some embodiments, the timer value used by the UE for the LTM candidate cell may be part of the LTM candidate cell configuration, or part of an LTM configuration for one or more LTM candidate cells (e.g., in fields / IEs / parameters related to early UL synchronization or early DL synchronization). In other embodiments, the timer value used by the UE for the LTM candidate cell may be received in the single command (e.g., MAC CE, PDCCH order, lean RRC message). In other embodiments, the timer value used by the UE for the LTM candidate cell may be the value of the time alignment timer (TAT) for the LTM candidate cell TA. However, the timer value used by the UE for the LTM candidate cell may also be different this TAT value.

[0193] In some embodiments, when the UE has activated a TCI state of an LTM candidate cell based on any of the single commands discussed above, the UE may later receive a further command (e.g., MAC CE) to deactivate the TCI state previously activated along with TA acquisition in the LTM candidate cell. In such case, the further command can override the single command, causing the UE to deactivate the previously activated TCI state for the LTM candidate cell.

[0194] In other embodiments, the UE may perform TA acquisition and TCI state activation at different times in response to multiple commands from the RAN. For example, a UE configured with at least one LTM candidate cell receives (e.g., from the UE’s serving RAN node) a first command (e.g., PDCCH order, MAC CE, RRC message, a single L3 protocol message, a single L2 protocol message, a single LI protocol message, etc.) to perform TA acquisition (or early UL synchronization) for an LTM candidate cell. The first command may include an identifier of the LTM candidate cell for which the UE should perform such actions. In some embodiments, the first command may also include one or more of the following:

[0195] • a RS (or beam) identifier, such as an SSB index associated with the LTM candidate cell; and

[0196] • an identifier of a TAG associated with the identified beam / RS in the LTM candidate cell.

[0197] In such embodiments, the UE performs TA acquisition by selecting a RA preamble and / or other resources associated with the RS identifier and transmits toward the LTM candidate cell using the selected RA preamble / resources. In response, the UE receives (e.g., from serving RAN node or target RAN node serving LTM candidate cell) a second command (e.g., MAC CE, RA response, PDCCH order, lean RRC message, etc.) to activate a TCI state for the LTM candidate cell. In response, the UE performs TCI state activation (or early DL synchronization) for the LTM candidate cell. The second command may also include the TA value for the LTM candidate cell.

[0198] In some of these embodiments, the TCI state activated by the UE for the LTM candidate cell has a QCL source RS (e.g., type D) that matches (or corresponds to) the RS identifier (e.g., SSB index) included with the first command. In such case, since it is based on parameters in the first command, it may be viewed that the UE triggers the TCI state activation based on the first command but it only executes the TCI state activation after receiving the second command. One benefit of these embodiments is that the UE only triggers early DL synchronization after it learns that early UL synchronization was successful based on reception of the second command (e.g., RA response to RA preamble).

[0199] In other of these embodiments, the second command may also include another TCI state for the LTM candidate cell (e.g., a separate DL TCI state or another UL / Joint TCI state), which is QCL’d with the same or another SSB of the LTM candidate cell.

[0200] In other of these embodiments, the second command is a RA response (RAR)-like message that includes a RA preamble ID (RAPID), and the UE activates the TCI state which has as QCL source (e.g., type D) the SSB index associated with the RA preamble identified in the RAPID field.

[0201] In some of these embodiments, when the UE receives the second command, the UE starts a timer. While the timer is running, the UE needs to maintain early DL synchronization with the LTM candidate cell, which may include various operations discussed above in relation to other embodiments. The same or similar conditions may be used to stop the timer as discussed above for embodiments that use a single command. Moreover, the timer value may be configured in any of the ways discussed above for embodiments that use a single command.

[0202] In different variants of these embodiments, the functionality of the first and second commands may be interchanged relative to the above description. In other words, the first command may cause the UE to activate TCI state for the LTM candidate cell and the second command may cause the UE to initiate TA acquisition for the LTM candidate.

[0203] In some embodiments, the first and second commands may be sent in different network signaling (e.g., first / second lean RRC messages, first / second MAC PDUs, etc.). Alternatively, the first and second commands may be sent in the same network signaling (e.g., different IES in same lean RRC message, different MAC CEs in MAC PDU, different fields in same LI signaling, etc.).

[0204] Various features of the embodiments described above correspond to various operations illustrated in Figures 10-11, which show exemplary methods (e.g., procedures) for a UE and a RAN node, respectively. In other words, various features of the operations described below correspond to various embodiments described above. Furthermore, the exemplary methods shown in Figures 10-11 can be used cooperatively to provide various benefits, advantages, and / or solutions to problems described herein. Although Figures 10-11 show specific blocks in particular orders, the operations of the exemplary methods can be performed in different orders than shown and can be combined and / or divided into blocks having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

[0205] In particular, Figure 10 shows an exemplary method (e.g., procedure) for a UE configured for LTM in a RAN, according to various embodiments of the present disclosure. The exemplary method can be performed by any appropriate UE (e.g., wireless device) such as described elsewhere herein.

[0206] The exemplary method includes the operations of block 1010, where the UE receives from a RAN node a single command for early synchronization with an LTM candidate cell. The single command includes an identifier of the LTM candidate cell and an identifier associated with a TCI state of the LTM candidate cell. The exemplary method also includes the operations of block 1020, where based on the single command, the UE performs early UL synchronization and early DL synchronization with the LTM candidate cell. In some embodiments, the identifier associated with the TCI state is a TCI state ID and performing early DL synchronization with the LTM candidate cell in block 1020 includes the operations of sub-block 1020a, where the UE activates, for the LTM candidate cell, a TCI state that is identified by the TCI state ID.

[0207] In other embodiments, the identifier associated with the TCI state is an identifier of a RS of the LTM candidate cell and performing early DL synchronization with the LTM candidate cell in block 1020 includes the following operations, labelled with corresponding sub-block numbers:

[0208] • (1020b) selecting, for the LTM candidate cell, a configured TCI state that has a quasicolocation (QCL) source RS that matches or corresponds to the identified RS; and

[0209] • (1020c) activating the selected TCI state.

[0210] In some of these embodiments, the identifier of the RS is a synchronization signal / PBCCH block (SSB) index or a channel state information (CSI) RS resource identifier.

[0211] In some of these embodiments, performing early DL synchronization in block 1020 also includes the following operations, labelled with corresponding sub-block numbers:

[0212] • (1020d) initiating a timer in response to receiving the single command; and

[0213] • (1020e) maintaining early DL synchronization with the LTM candidate cell while the timer is running and not expired.

[0214] In some variants of these embodiments, performing early DL synchronization in block 1020 also includes the operations of sub-block 1020f, where the UE stops the timer while it is running, in response to any of the following: receiving an LTM cell switch command, initiating an LTM cell switch based on one or more execution conditions being fulfilled, receiving an L3 handover command, and receiving a L3 message associated with the LTM candidate cell.

[0215] In some variants of these embodiments, the timer is initiated with one of the following timer values: a timer value included with the single command, a timer value included in a configuration for the LTM candidate cell, or a time alignment timer (TAT) value associated with early UL synchronization to the LTM candidate cell.

[0216] In some of these embodiments, the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single timing advance group (TAG). In such case, performing early DL synchronization to the LTM candidate cell in block 1020 also includes the operations of sub-block 1020g, where the UE activates UL or joint TCI states in other of the plurality of configured LTM candidate cells in the TAG.

[0217] In some embodiments, the identifier associated with the TCI state is a TCI state ID and performing early UL synchronization to the LTM candidate cell in block 1020 includes the following operations, labelled with corresponding sub-block numbers:

[0218] • (1020h) selecting a RS, of the LTM candidate cell, that matches or corresponds to a QCL source RS for the TCI state identified by the TCI state ID;

[0219] • (1020i) selecting, for the LTM candidate cell, one or more RA parameters that are associated with the selected RS; and

[0220] • (1020k) transmitting a RA preamble towards the LTM candidate cell in accordance with the selected RA parameters.

[0221] In other embodiments, the identifier associated with the TCI state is an identifier of a RS of the LTM candidate cell and performing early UL synchronization to the LTM candidate cell in block 1020 includes the following operations, labelled with corresponding sub-block numbers:

[0222] • (1020j) selecting, for the LTM candidate cell, one or more RA parameters that are associated with the identified RS; and

[0223] • (1020k) transmitting a RA preamble towards the LTM candidate cell in accordance with the selected RA parameters.

[0224] In some of these embodiments, the selected RA parameters includes one or more of the following: the RA preamble, and physical RA channel (PRACH) time / frequency resources.

[0225] In some of these embodiments, the early UL synchronization and the early DL synchronization are performed responsive to the single command. In other of these embodiments, the early UL synchronization is performed in block 1020 responsive to the single command and also includes the operations of sub-block 1020m, where the UE receives an indication that the early UL synchronization to the LTM candidate cell was successful. In such case, the UE performs the early DL synchronization (including any applicable sub-blocks in block 1020) in response to the indication received in sub-block 1020m. In some variants of these embodiments, one or more of the following applies:

[0226] • the indication that the early UL synchronization was successful is a RA response to the RA preamble transmitted by the UE; and

[0227] • the indication that the early UL synchronization was successful includes a timing advance (TA) value for the LTM candidate cell;

[0228] • the indication that the early UL synchronization was successful includes a further identifier associated with a further TCI state of the LTM candidate cell, based on which the early DL synchronization is performed.

[0229] In some embodiments, the single command is one of the following:

[0230] • a medium access control (MAC) control element (CE);

[0231] • a MAC protocol data unit (PDU);

[0232] • a physical DL control channel (PDCCH) order;

[0233] • a lean radio resource control (RRC) message; • a layer-2 (L2) signaling message; or

[0234] • a layer- 1 (LI) signaling message.

[0235] In some of these embodiments, the MAC PDU includes first and second MAC CEs, the first MAC CE corresponds to a command to perform early UL synchronization, and the second MAC CE corresponds to a command to perform early DL synchronization.

[0236] In other of these embodiments, the single command is a MAC CE for early DL synchronization and one of the following indicates that the UE should also perform early UL synchronization in response to the MAC CE: a format of the MAC CE, a logical channel or logical channel group associated with the MAC CE, or content of a field in the MAC CE.

[0237] In other of these embodiments, the single command is a PDCCH order for early UL synchronization and one of the following indicates that the UE should also perform early DL synchronization in response to the PDCCH order: a format of the PDCCH order, or content of a field in the PDCCH order.

[0238] In some embodiments, the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single timing advance group (TAG), and the early UL synchronization is performed for all of the plurality of configured LTM candidate cells in the TAG.

[0239] In addition, Figure 11 shows an exemplary method (e.g., procedure) for a RAN node configured to facilitate LTM for UEs, according to various embodiments of the present disclosure. The exemplary method can be performed by a RAN node (e.g., base station, eNB, gNB, ng-eNB, DU, etc.) such as described elsewhere herein.

[0240] The exemplary method includes the operations of block 1120, where the RAN node sends, to a UE via a source cell provided by the RAN node, a single command for early synchronization with an LTM candidate cell. The single command includes an identifier of the LTM candidate cell and an identifier associated with a TCI state of the LTM candidate cell. The single command facilitates both early UL synchronization and early DL synchronization of the UE with the LTM candidate cell.

[0241] In some embodiments, the identifier associated with the TCI state is a TCI state ID, such that early DL synchronization of the UE with the LTM candidate is based on UE activation of a TCI state, for the LTM candidate cell, that is identified by the TCI state ID.

[0242] In other embodiments, the identifier associated with the TCI state is an identifier of a RS of the LTM candidate cell, such that early DL synchronization of the UE with the LTM candidate is based on UE activation of a configured TCI state, for the LTM candidate cell, that has a QCL source RS that matches or corresponds to the identified RS. In some of these embodiments, the identifier of the RS is one of the following: an SSB index, or a CSI RS resource identifier. In some of these embodiments, early DL synchronization of the UE with the LTM candidate is further based on one of the following: a timer value sent to the UE in the single command, a timer value sent to the UE in a configuration for the LTM candidate cell, or a TAT value associated with early UL synchronization to the LTM candidate cell. The UE may use any of these timer values as described above in relation to UE embodiments.

[0243] In some of these embodiments, the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single TAG, and early DL synchronization of the UE with the LTM candidate cell is further based on UE activation of UL or joint TCI states in other of the plurality of configured LTM candidate cells in the TAG.

[0244] In some embodiments, the identifier associated with the TCI state is a TCI state ID and early UL synchronization of the UE with the LTM candidate cell is based on the following:

[0245] • a RS, of the LTM candidate cell, that matches or corresponds to a QCL source RS for the TCI state identified by the TCI state ID;

[0246] • one or more RA parameters, for the LTM candidate cell, that are associated with the selected RS; and

[0247] • a RA preamble transmitted by the UE towards the LTM candidate cell in accordance with the RA parameters.

[0248] In other embodiments, the identifier associated with the TCI state is an identifier of a RS of the LTM candidate cell and early UL synchronization of the UE with the LTM candidate cell is based on the following:

[0249] • one or more RA parameters, for the LTM candidate cell, that are associated with the identified RS; and

[0250] • a RA preamble transmitted by the UE towards the LTM candidate cell in accordance with the RA parameters.

[0251] In some of these embodiments, the RA parameters include one or more of the following: the RA preamble, and PRACH time / frequency resources.

[0252] In some of these embodiments, the early UL synchronization and the early DL synchronization of the UE are responsive to the single command. In other of these embodiments, the early UL synchronization of the UE is responsive to the single command and the exemplary method also includes the operations of block 1120, where the RAN node sends to the UE an indication that the early UL synchronization to the LTM candidate cell was successful. In such case, the early DL synchronization of the UE is responsive to the indication. In some variants of these embodiments, one or more of the following applies:

[0253] • the indication that the early UL synchronization was successful is a RA response to the RA preamble transmitted by the UE; • the indication that the early UL synchronization was successful includes a TA value for the LTM candidate cell; and

[0254] • the indication that the early UL synchronization was successful includes a further identifier associated with a further TCI state of the LTM candidate cell, based on which the early DL synchronization is performed.

[0255] In some embodiments, the single command is one of the following: a MAC CE, a MAC PDU, a PDCCH order, a lean RRC message, an L2 signaling message, or an LI signaling message.

[0256] In some of these embodiments, the MAC PDU includes first and second MAC CEs, the first MAC CE corresponds to a command to perform early UL synchronization, and the second MAC CE corresponds to a command to perform early DL synchronization.

[0257] In other of these embodiments, the single command is a MAC CE for early DL synchronization and one of the following indicates that the UE should also perform early UL synchronization in response to the MAC CE: a format of the MAC CE, a logical channel or logical channel group associated with the MAC CE, or content of a field in the MAC CE.

[0258] In other of these embodiments, the single command is a PDCCH order for early UL synchronization and one of the following indicates that the UE should also perform early DL synchronization in response to the PDCCH order: a format of the PDCCH order, or content of a field in the PDCCH order.

[0259] In some embodiments, the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single TAG and the early UL synchronization of the UE is with all of the plurality of configured LTM candidate cells in the TAG.

[0260] Although various embodiments are described above in terms of methods, techniques, and / or procedures, the person of ordinary skill will readily comprehend that such methods, techniques, and / or procedures can be embodied by various combinations of hardware and software in various systems, communication devices, computing devices, control devices, apparatuses, non-transitory computer-readable media, computer program products, etc.

[0261] Figure 12 shows an example of a communication system 1200 in accordance with some embodiments. In this example, communication system 1200 includes a telecommunication network 1202 that includes an access network 1204 (e.g., RAN) and a core network 1206, which includes one or more core network nodes 1208. Access network 1204 includes one or more access network nodes, such as network nodes 1210a-b (one or more of which may be generally referred to as network nodes 1210), or any other similar 3 GPP access nodes or non-3GPP access points. Moreover, as will be appreciated by those of skill in the art, a network node is not necessarily limited to an implementation in which a radio portion and a baseband portion are supplied and integrated by a single vendor. Thus, it will be understood that network nodes include disaggregated implementations or portions thereof. For example, in some embodiments, telecommunication network 1202 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 1202 that supports an ORAN specification (e.g., a specification published by the O-RAN Alliance, or any similar organization) and may operate alone or together with other nodes to implement one or more functionalities of any node in telecommunication network 1202, including one or more network nodes 1210 and / or core network nodes 1208.

[0262] Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O-CU- CP) or an O-CU user plane (O-CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wl, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an O-2 interface defined by the O-RAN Alliance or comparable technologies. Network nodes 1210 facilitate direct or indirect connection of UEs, such as by connecting UEs 1212a-d (one or more of which may be generally referred to as UEs 1212) to core network 1206 over one or more wireless connections.

[0263] Example wireless communications over a wireless connection include transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, communication system 1200 may include any number of wired or wireless networks, network nodes, UEs, and / or any other components or systems that may facilitate or participate in the communication of data and / or signals whether via wired or wireless connections. Communication system 1200 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0264] UEs 1212 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with network nodes 1210 and other communication devices. Similarly, network nodes 1210 are arranged, capable, configured, and / or operable to communicate directly or indirectly with UEs 1212 and / or with other network nodes or equipment in telecommunication network 1202 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in telecommunication network 1202.

[0265] In the depicted example, core network 1206 connects network nodes 1210 to one or more hosts, such as host 1216. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. Core network 1206 includes one or more core network nodes (e.g., 1208) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and / or hosts, such that the descriptions thereof are generally applicable to the corresponding components of core network node 1208. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealing function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and / or a User Plane Function (UPF).

[0266] Host 1216 may be under the ownership or control of a service provider other than an operator or provider of access network 1204 and / or telecommunication network 1202, and may be operated by the service provider or on behalf of the service provider. Host 1216 may host a variety of applications to provide one or more service. Examples of such applications include live and pre-recorded audio / video content, data collection services such as retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

[0267] As a whole, communication system 1200 of Figure 12 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and / or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and / or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

[0268] In some examples, telecommunication network 1202 is a cellular network that implements 3 GPP standardized features. Accordingly, telecommunication network 1202 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 1202. For example, telecommunication network 1202 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and / or Massive Machine Type Communication (mMTC) / Massive loT services to yet further UEs.

[0269] In some examples, UEs 1212 are configured to transmit and / or receive information without direct human interaction. For instance, a UE may be designed to transmit information to access network 1204 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 1204. Additionally, a UE may be configured for operating in single- or multi-RAT or multi-standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e., being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC).

[0270] In the example, hub 1214 communicates with access network 1204 to facilitate indirect communication between one or more UEs (e.g., 1212c and / or 1212d) and network nodes (e.g., network node 1210b). In some examples, hub 1214 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 1214 may be a broadband router enabling access to core network 1206 for the UEs. As another example, hub 1214 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 1210, or by executable code, script, process, or other instructions in hub 1214. As another example, hub 1214 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, hub 1214 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 1214 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 1214 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, hub 1214 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0271] Hub 1214 may have a constant / persistent or intermittent connection to network node 1210b. Hub 1214 may also allow for a different communication scheme and / or schedule between hub 1214 and UEs (e.g., 1212c and / or 1212d), and between hub 1214 and core network 1206. In other examples, hub 1214 is connected to core network 1206 and / or one or more UEs via a wired connection. Moreover, hub 1214 may be configured to connect to an M2M service provider over access network 1204 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 1210 while still connected via hub 1214 via a wired or wireless connection. In some embodiments, hub 1214 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to network node 1210b. In other embodiments, hub 1214 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1210b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0272] In some embodiments, any of network nodes 1210 may be configured to perform operations attributed to a RAN node in embodiments described above, including the exemplary method shown in Figure 11. In some embodiments, any of UEs 1212 may be configured to perform operations attributed to a UE in embodiments described above, including the exemplary method shown in Figure 10.

[0273] Figure 13 shows a UE 1300 in accordance with some embodiments. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by 3 GPP, including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0274] A UE may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and / or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter). UE 1300 includes processing circuitry 1302 that is operatively coupled via a bus 1304 to an input / output interface 1306, a power source 1308, a memory 1310, a communication interface 1312, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 13. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0275] Processing circuitry 1302 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in memory 1310. Processing circuitry 1302 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, field- programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general-purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, processing circuitry 1302 may include multiple central processing units (CPUs).

[0276] In the example, input / output interface 1306 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and / or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into UE 1300. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

[0277] In some embodiments, power source 1308 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. Power source 1308 may further include power circuitry for delivering power from power source 1308 itself, and / or an external power source, to the various parts of UE 1300 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of power source 1308. Power circuitry may perform any formatting, converting, or other modification to the power from power source 1308 to make the power suitable for the respective components of UE 1300 to which power is supplied.

[0278] Memory 1310 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, memory 1310 includes one or more application programs 1314, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1316. Memory 1310 may store, for use by UE 1300, any of a variety of various operating systems or combinations of operating systems.

[0279] Memory 1310 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and / or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ Memory 1310 may allow UE 1300 to access instructions, application programs and the like, stored on transitory or non- transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in memory 1310, which may be or comprise a device-readable storage medium.

[0280] Processing circuitry 1302 may be configured to communicate with an access network or other network using communication interface 1312. Communication interface 1312 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1322. Communication interface 1312 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 1318 and / or a receiver 1320 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmitter 1318 and receiver 1320 may be coupled to one or more antennas (e.g., antenna 1322) and may share circuit components, software, or firmware, or alternatively be implemented separately. In the illustrated embodiment, communication functions of communication interface 1312 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and / or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol / internet protocol (TCP / IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0281] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1312, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0282] As another example, a UE comprises an actuator, a motor, or a switch, related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or to a robotic arm performing a medical procedure according to the received input.

[0283] A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or Virtual Reality (VR), a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and / or software in dependence of the intended application of the loT device in addition to other components as described in relation to UE 1300 shown in Figure 13.

[0284] As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and / or measurements, and transmits the results of such monitoring and / or measurements to another UE and / or a network node. The UE may in this case be an M2M device, which may in a 3 GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.

[0285] In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g., by controlling an actuator) to increase or decrease the drone’s speed. The first and / or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators.

[0286] In some embodiments, UE 1300 may be configured to perform operations attributed to a UE in various embodiments described above, including the exemplary method shown in Figure 10.

[0287] Figure 14 shows a network node 1400 in accordance with some embodiments. Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (e.g., radio base stations, Node Bs, eNBs, gNBs), and 0-RAN nodes or components of an 0-RAN node (e.g, 0-RU, 0-DU, O-CU).

[0288] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units, distributed units (e.g, in an 0-RAN access node) and / or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

[0289] Other examples of network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell / multicast coordination entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and / or Minimization of Drive Tests (MDTs).

[0290] Network node 1400 includes processing circuitry 1402, memory 1404, communication interface 1406, and power source 1408. Network node 1400 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which network node 1400 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, network node 1400 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1404 for different RATs) and some components may be reused (e.g., a same antenna 1410 may be shared by different RATs). Network node 1400 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1400, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 1400.

[0291] Processing circuitry 1402 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other network node 1400 components, such as memory 1404, to provide network node 1400 functionality.

[0292] In some embodiments, processing circuitry 1402 includes a system on a chip (SOC). In some embodiments, processing circuitry 1402 includes one or more of radio frequency (RF) transceiver circuitry 1412 and baseband processing circuitry 1414. In some embodiments, RF transceiver circuitry 1412 and baseband processing circuitry 1414 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1412 and baseband processing circuitry 1414 may be on the same chip or set of chips, boards, or units.

[0293] Memory 1404 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computer-executable memory devices that store information, data, and / or instructions that may be used by processing circuitry 1402. Memory 1404 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and / or other instructions (collected denoted computer program 1404a, which may be in the form of a computer program product) capable of being executed by processing circuitry 1402 and utilized by network node 1400. Memory 1404 may be used to store any calculations made by processing circuitry 1402 and / or any data received via communication interface 1406. In some embodiments, processing circuitry 1402 and memory 1404 is integrated.

[0294] Communication interface 1406 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, communication interface 1406 comprises port(s) / terminal(s) 1416 to send and receive data, for example to and from a network over a wired connection. Communication interface 1406 also includes radio frontend circuitry 1418 that may be coupled to, or in certain embodiments a part of, antenna 1410. Radio front-end circuitry 1418 comprises filters 1420 and amplifiers 1422. Radio front-end circuitry 1418 may be connected to an antenna 1410 and processing circuitry 1402. The radio front-end circuitry may be configured to condition signals communicated between antenna 1410 and processing circuitry 1402. Radio front-end circuitry 1418 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 1418 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1420 and / or amplifiers 1422. The radio signal may then be transmitted via antenna 1410. Similarly, when receiving data, antenna 1410 may collect radio signals which are then converted into digital data by radio front-end circuitry 1418. The digital data may be passed to processing circuitry 1402. In other embodiments, the communication interface may comprise different components and / or different combinations of components. In certain alternative embodiments, network node 1400 does not include separate radio front-end circuitry 1418, instead, processing circuitry 1402 includes radio front-end circuitry and is connected to antenna 1410. Similarly, in some embodiments, all or some of RF transceiver circuitry 1412 is part of communication interface 1406. In still other embodiments, communication interface 1406 includes one or more ports or terminals 1416, radio front-end circuitry 1418, and RF transceiver circuitry 1412, as part of a radio unit (not shown), and communication interface 1406 communicates with baseband processing circuitry 1414, which is part of a digital unit (not shown).

[0295] Antenna 1410 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. Antenna 1410 may be coupled to radio front-end circuitry 1418 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, antenna 1410 is separate from network node 1400 and connectable to network node 1400 through an interface or port.

[0296] Antenna 1410, communication interface 1406, and / or processing circuitry 1402 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node. Any information, data and / or signals may be received from a UE, another network node and / or any other network equipment. Similarly, antenna 1410, communication interface 1406, and / or processing circuitry 1402 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and / or signals may be transmitted to a UE, another network node and / or any other network equipment.

[0297] Power source 1408 provides power to the various components of network node 1400 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 1408 may further comprise, or be coupled to, power management circuitry to supply the components of network node 1400 with power for performing the functionality described herein. For example, network node 1400 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of power source 1408. As a further example, power source 1408 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0298] Embodiments of network node 1400 may include additional components beyond those shown in Figure 14 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, network node 1400 may include user interface equipment to allow input of information into network node 1400 and to allow output of information from network node 1400. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1400.

[0299] In some embodiments, network node 1400 may be configured to perform operations attributed to a RAN node in embodiments described above, including the exemplary method shown in Figure 11.

[0300] Figure 15 is a block diagram illustrating a virtualization environment 1500 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1500 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized. In some embodiments, the virtualization environment 1500 includes components defined by the O-RAN Alliance, such as an O-Cloud environment orchestrated by a Service Management and Orchestration Framework via an O-2 interface.

[0301] Applications 1502 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1500 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein. For example, a virtual node 1502 may be configured to perform operations attributed to a RAN node in embodiments described above, including the exemplary method shown in Figure 11.

[0302] Hardware 1504 includes processing circuitry, memory that stores software and / or instructions (collected denoted computer program 1504a, which may be in the form of a computer program product) executable by hardware processing circuitry, and / or other hardware devices as described herein, such as a network interface, input / output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1506 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1508a-b (one or more of which may be generally referred to as VMs 1508), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. Virtualization layer 1506 may present a virtual operating platform that appears like networking hardware to the VMs 1508.

[0303] VMs 1508 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1506. Different embodiments of the instance of a virtual appliance 1502 may be implemented on one or more of VMs 1508, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as network function virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

[0304] In the context of NFV, each VM 1508 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each VM 1508, and that part of hardware 1504 that executes that VM, be it hardware dedicated to that VM and / or hardware shared by that VM with others of the VMs, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 1508 on top of the hardware 1504 and corresponds to the application 1502.

[0305] Hardware 1504 may be implemented in a standalone network node with generic or specific components. Hardware 1504 may implement some functions via virtualization. Alternatively, hardware 1504 may be part of a larger cluster of hardware (e.g., such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration function 1510, which, among others, oversees lifecycle management of applications 1502. In some embodiments, hardware 1504 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signaling can be provided with the use of a control system 1512 which may alternatively be used for communication between hardware nodes and radio units.

[0306] The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures that, although not explicitly shown or described herein, embody the principles of the disclosure and can be thus within the spirit and scope of the disclosure. Various embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art.

[0307] The term unit, as used herein, can have conventional meaning in the field of electronics, electrical devices and / or electronic devices and can include, for example, electrical and / or electronic circuitry, devices, modules, processors, memories, logic solid state and / or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and / or displaying functions, and so on, as such as those that are described herein.

[0308] Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processor (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according to one or more embodiments of the present disclosure.

[0309] As described herein, device and / or apparatus can be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor. Furthermore, functionality of a device or apparatus can be implemented by any combination of hardware and software. A device or apparatus can also be regarded as an assembly of multiple devices and / or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses can be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person.

[0310] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0311] In addition, certain terms used in the present disclosure, including the specification and drawings, can be used synonymously in certain instances (e.g., “data” and “information”). It should be understood that although such terms may be used synonymously herein, there may be instances herein where such terms are not intended to be used synonymously.

[0312] Embodiments of the techniques and apparatus described herein also include, but are not limited to, the following enumerated examples:

[0313] Al . A method for a user equipment (UE) configured for layer- 1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) in a radio access network (RAN), the method comprising: receiving, from a RAN node, a single command for early synchronization with an LTM candidate cell, wherein the single command includes an identifier of the LTM candidate cell and an identifier associated with a transmission configuration indicator (TCI) state of the LTM candidate cell; and based on the single command, performing early uplink (UL) synchronization and early downlink (DL) synchronization with the LTM candidate cell.

[0314] A2. The method of embodiment Al, wherein the identifier associated with the TCI state is a TCI state identifier (ID), and performing early DL synchronization with the LTM candidate cell comprises activating a TCI state, for the LTM candidate cell, that is identified by the TCI state ID.

[0315] A2a. The method of embodiment Al, wherein the identifier associated with the TCI state is an identifier of a reference signal (RS) of the LTM candidate cell, and performing early DL synchronization with the LTM candidate cell comprises: selecting a configured TCI state, for the LTM candidate cell, that has a quasi -colocation (QCL) source RS that matches or corresponds to the identified RS; and activating the selected TCI state.

[0316] A2b. The method of claim A2a, wherein the identifier of the RS is one of the following: a synchronization signal / PBCCH block (SSB) index, or a channel state information (CSI) RS resource identifier. A2c. The method of any of embodiments A2-A2b, wherein performing early DL synchronization further comprises: initiating a timer in response to receiving the single command; and maintaining early DL synchronization with the LTM candidate cell while the timer is running and not expired.

[0317] A2d. The method of embodiment A2c, wherein performing early DL synchronization further comprises stopping the timer while it is running, in response to any of the following: receiving an LTM cell switch command, initiating an LTM cell switch based on one or more execution conditions being fulfilled, and receiving a layer-3 (L3) handover command, and receiving a L3 message associated with the LTM candidate cell.

[0318] A2e. The method of any of embodiments A2c-A2d, wherein the timer is initiated with one of the following timer values: a timer value included with the single command, a timer value included in a configuration for the LTM candidate cell, or a time alignment timer (TAT) value associated with early UL synchronization to the LTM candidate cell.

[0319] A2f. The method of any of embodiments A2-A2e, wherein the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single timing advance group (TAG), and performing early DL synchronization to the LTM candidate cell further comprises activating uplink (UL) or joint TCI states in other of the plurality of configured LTM candidate cells in the TAG.

[0320] A3. The method of any of embodiments Al-A2f, wherein the identifier associated with the TCI state is a TCI state identifier (ID), and performing early UL synchronization to the LTM candidate cell comprises: selecting a reference signal (RS), of the LTM candidate cell, that matches or corresponds to a quasi-colocation (QCL) source RS for the TCI state identified by the TCI state ID; selecting one or more random access (RA) parameters, for the LTM candidate cell, that are associated with the selected RS; and transmitting a RA preamble towards the LTM candidate cell in accordance with the selected RA parameters.

[0321] A3a. The method of any of embodiments Al-A2e, wherein the identifier associated with the TCI state is an identifier of a reference signal (RS) of the LTM candidate cell, and performing early UL synchronization with the LTM candidate cell comprises: selecting one or more random access (RA) parameters, for the LTM candidate cell, that are associated with the identified RS; and transmitting a RA preamble towards the LTM candidate cell in accordance with the selected RA parameters.

[0322] A3b. The method of any of embodiments A3 -A3 a, wherein the selected RA parameters includes one or more of the following: the RA preamble, and physical RA channel (PRACH) time / frequency resources.

[0323] A3c. The method of any of embodiments A3-A3b, wherein the early UL synchronization and the early DL synchronization are performed responsive to the single command.

[0324] A3d. The method of any of embodiments A3-A3b, wherein: the early UL synchronization is performed responsive to the single command and further comprises receiving an indication that the early UL synchronization to the LTM candidate cell was successful; and performing the early DL synchronization is performed in response to the received indication.

[0325] A3e. The method of embodiment A3d, wherein one or more of the following applies: the indication that the early UL synchronization was successful is a random access (RA) response to the RA preamble transmitted by the UE; and the indication that the early UL synchronization was successful includes a timing advance (TA) value for the LTM candidate cell; the indication that the early UL synchronization was successful includes a further identifier associated with a further TCI state of the LTM candidate cell, based on which the early DL synchronization is performed.

[0326] A4. The method of any of claims Al-A3e, wherein the single command is one of the following: a medium access control (MAC) control element (CE); a MAC protocol data unit (PDU); a physical DL control channel (PDCCH) order; a lean radio resource control (RRC) message; a layer-2 (L2) signaling message; or a layer- 1 (LI) signaling message.

[0327] A4a. The method of embodiment A4, wherein the MAC PDU includes first and second MAC CEs, the first MAC CE corresponds to a command to perform early UL synchronization, and the second MAC CE corresponds to a command to perform early DL synchronization.

[0328] A4b. The method of embodiment A4, wherein the single command is a MAC CE for early DL synchronization and one of the following indicates that the UE should also perform early UL synchronization in response to the MAC CE: a format of the MAC CE, a logical channel or logical channel group associated with the MAC CE, or content of a field in the MAC CE.

[0329] A4c. The method of embodiment A4, wherein the single command is a PDCCH order for early UL synchronization and one of the following indicates that the UE should also perform early DL synchronization in response to the PDCCH order: a format of the PDCCH order, or content of a field in the PDCCH order.

[0330] A5. The method of any of embodiments Al-A4c, wherein the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single timing advance group (TAG), and the early UL synchronization is performed for all of the plurality of configured LTM candidate cells in the TAG.

[0331] BL A method for a radio access network (RAN) node configured to facilitate layer- 1 / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), the method comprising: sending, to a UE via a source cell provided by the RAN node, a single command for early synchronization with an LTM candidate cell, wherein: the single command includes an identifier of the LTM candidate cell and an identifier associated with a transmission configuration indicator (TCI) state of the LTM candidate cell; and the single command facilitates both early uplink (UL) synchronization and early downlink (DL) synchronization of the UE with the LTM candidate cell.

[0332] B2. The method of embodiment Bl, wherein the identifier associated with the TCI state is a TCI state identifier (ID), such that early DL synchronization of the UE with the LTM candidate is based on activation of a TCI state, for the LTM candidate cell, that is identified by the TCI state ID.

[0333] B2a. The method of embodiment Al, wherein the identifier associated with the TCI state is an identifier of a reference signal (RS) of the LTM candidate cell, such that early DL synchronization of the UE with the LTM candidate is based on activation of a configured TCI state, for the LTM candidate cell, that has a quasi-colocation (QCL) source RS that matches or corresponds to the identified RS.

[0334] B2b. The method of claim B2a, wherein the identifier of the RS is one of the following: a synchronization signal / PBCCH block (SSB) index, or a channel state information (CSI) RS resource identifier.

[0335] B2c. The method of any of embodiments A2-A2b, wherein early DL synchronization of the UE with the LTM candidate is further based on one of the following: a timer value sent to the UE in the single command, a timer value sent to the UE in a configuration for the LTM candidate cell, or a time alignment timer (TAT) value associated with early UL synchronization to the LTM candidate cell.

[0336] B2d. The method of any of embodiments B2-B2c, wherein the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single timing advance group (TAG), and early DL synchronization of the UE with the LTM candidate cell is further based on activation of uplink (UL) or joint TCI states in other of the plurality of configured LTM candidate cells in the TAG.

[0337] B3. The method of any of embodiments Bl-B2d, wherein the identifier associated with the TCI state is a TCI state identifier (ID), and early UL synchronization of the UE with the LTM candidate cell is based on the following: a reference signal (RS), of the LTM candidate cell, that matches or corresponds to a quasi-colocation (QCL) source RS for the TCI state identified by the TCI state ID; one or more random access (RA) parameters, for the LTM candidate cell, that are associated with the selected RS; and a RA preamble transmitted by the UE towards the LTM candidate cell in accordance with the RA parameters. B3a. The method of any of embodiments Bl-B2d, wherein the identifier associated with the TCI state is an identifier of a reference signal (RS) of the LTM candidate cell, and early UL synchronization of the UE with the LTM candidate cell is based on the following: one or more random access (RA) parameters, for the LTM candidate cell, that are associated with the identified RS; and a RA preamble transmitted by the UE towards the LTM candidate cell in accordance with the RA parameters.

[0338] B3b. The method of any of embodiments A3 -A3 a, wherein the RA parameters include one or more of the following: the RA preamble, and physical RA channel (PRACH) time / frequency resources.

[0339] B3c. The method of any of embodiments B3-B3b, wherein the early UL synchronization and the early DL synchronization of the UE are responsive to the single command.

[0340] B3d. The method of any of embodiments B3-B3b, wherein: the early UL synchronization of the UE is responsive to the single command and the method further comprises sending to the UE an indication that the early UL synchronization to the LTM candidate cell was successful; and the early DL synchronization of the UE is responsive to the indication.

[0341] B3e. The method of embodiment B3d, wherein one or more of the following applies: the indication that the early UL synchronization was successful is a random access (RA) response to the RA preamble transmitted by the UE; and the indication that the early UL synchronization was successful includes a timing advance (TA) value for the LTM candidate cell; the indication that the early UL synchronization was successful includes a further identifier associated with a further TCI state of the LTM candidate cell, based on which the early DL synchronization is performed.

[0342] B4. The method of any of claims Bl-B3e, wherein the single command is one of the following: a medium access control (MAC) control element (CE); a MAC protocol data unit (PDU); a physical DL control channel (PDCCH) order; a lean radio resource control (RRC) message; a layer-2 (L2) signaling message; or a layer- 1 (LI) signaling message.

[0343] B4a. The method of embodiment B4, wherein the MAC PDU includes first and second MAC CEs, the first MAC CE corresponds to a command to perform early UL synchronization, and the second MAC CE corresponds to a command to perform early DL synchronization.

[0344] B4b. The method of embodiment B4, wherein the single command is a MAC CE for early DL synchronization and one of the following indicates that the UE should also perform early UL synchronization in response to the MAC CE: a format of the MAC CE, a logical channel or logical channel group associated with the MAC CE, or content of a field in the MAC CE.

[0345] B4c. The method of embodiment B4, wherein the single command is a PDCCH order for early UL synchronization and one of the following indicates that the UE should also perform early DL synchronization in response to the PDCCH order: a format of the PDCCH order, or content of a field in the PDCCH order.

[0346] B5. The method of any of embodiments Bl-B4c, wherein the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single timing advance group (TAG), and the early UL synchronization of the UE is with all of the plurality of configured LTM candidate cells in the TAG.

[0347] CL A user equipment (UE) configured for layer- l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE comprising: communication interface circuitry configured to communicate with RAN nodes; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of any of embodiments A1-A5.

[0348] C2. A user equipment (UE) configured for layer- l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE being further configured to perform operations corresponding to the methods of any of embodiments A1-A5. C3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured for layer- l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments A1-A5.

[0349] C4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of user equipment (UE) configured for layer- 1 / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments A1-A5.

[0350] DI . A radio access network (RAN) node configured to facilitate layer- l / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), the RAN node comprising: communication interface circuitry configured to communicate with UEs and with other RAN nodes; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of any of embodiments B1-B5.

[0351] D2. A radio access network (RAN) node configured to facilitate layer- l / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), the RAN node being further configured to perform operations corresponding to the methods of any of embodiments B1-B5.

[0352] D3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a radio access network (RAN) node configured to facilitate layer- l / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), configure the RAN node to perform operations corresponding to the methods of any of embodiments B1-B5.

[0353] D4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a radio access network (RAN) node configured to facilitate layer- l / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), configure the RAN node to perform operations corresponding to the methods of any of embodiments B1-B5.

Claims

CLAIMS1. A method for a user equipment, UE, configured for layer- l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN, the method comprising: receiving (1010), from a RAN node, a single command for early synchronization with an LTM candidate cell, wherein the single command includes an identifier of the LTM candidate cell and an identifier associated with a transmission configuration indicator, TCI, state of the LTM candidate cell; and based on the single command, performing (1020) early uplink, UL, synchronization and early downlink, DL, synchronization with the LTM candidate cell.

2. The method of claim 1, wherein the identifier associated with the TCI state is a TCI state identifier, ID, and performing (1020) early DL synchronization with the LTM candidate cell comprises activating (1020a), for the LTM candidate cell, a TCI state identified by the TCI state ID.

3. The method of claim 1, wherein the identifier associated with the TCI state is an identifier of a reference signal, RS, of the LTM candidate cell, and performing (1020) early DL synchronization with the LTM candidate cell comprises: selecting (1020b), for the LTM candidate cell, a configured TCI state that has a quasicolocation, QCL, source RS that matches or corresponds to the identified RS; and activating (1020c) the selected TCI state.

4. The method of claim 3, wherein the identifier of the RS is one of the following: a synchronization signal / PBCCH block, SSB, index; or a channel state information, CSI, RS resource identifier.

5. The method of any of claims 2-4, wherein performing (1020) early DL synchronization further comprises: initiating (1020d) a timer in response to receiving the single command; and maintaining (1020e) early DL synchronization with the LTM candidate cell while the timer is running and not expired.

6. The method of claim 5, wherein performing (1020) early DL synchronization further comprises stopping ( 1020f) the timer while it is running, in response to any of the following:receiving an LTM cell switch command, initiating an LTM cell switch based on one or more execution conditions being fulfilled, receiving a layer-3, L3, handover command, and receiving a L3 message associated with the LTM candidate cell.

7. The method of any of claims 5-6, wherein the timer is initiated with one of the following timer values: a timer value included with the single command, a timer value included in a configuration for the LTM candidate cell, or a time alignment timer, TAT, value associated with early UL synchronization to the LTM candidate cell.

8. The method of any of claims 2-7, wherein the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single timing advance group, TAG, and performing (1020) early DL synchronization to the LTM candidate cell further comprises activating (1020g) UL or joint TCI states for other of the plurality of configured LTM candidate cells in the TAG.

9. The method of any of claims 1-8, wherein the identifier associated with the TCI state is a TCI state identifier, ID, and performing (1020) early UL synchronization to the LTM candidate cell comprises: selecting (1020h) a reference signal, RS, of the LTM candidate cell, that matches or corresponds to a quasi -colocation, QCL, source RS for the TCI state identified by the TCI state ID; selecting ( 1020i), for the LTM candidate cell, one or more random access, RA, parameters associated with the selected RS; and transmitting (1020k) a RA preamble towards the LTM candidate cell in accordance with the selected RA parameters.

10. The method of any of claims 1-8, wherein the identifier associated with the TCI state is an identifier of a reference signal, RS, of the LTM candidate cell, and performing (1020) early UL synchronization with the LTM candidate cell comprises: selecting ( 1020j), for the LTM candidate cell, one or more random access, RA, parameters that are associated with the identified RS; and transmitting (1020k) a RA preamble towards the LTM candidate cell in accordance with the selected RA parameters.

11. The method of any of claims 10-11, wherein the selected RA parameters includes one or more of the following: the RA preamble; and physical RA channel, PRACH, time / frequency resources.

12. The method of any of claims 10-12, wherein the early UL synchronization and the early DL synchronization are performed responsive to the single command.

13. The method of any of claims 10-12, wherein: the early UL synchronization is performed responsive to the single command and further comprises receiving (1020m) an indication that the early UL synchronization to the LTM candidate cell was successful; and the early DL synchronization is performed in response to the received indication.

14. The method of claim 13, wherein one or more of the following applies: the indication that the early UL synchronization was successful is a RA response to the RA preamble transmitted by the UE; the indication that the early UL synchronization was successful includes a timing advance, TA, value for the LTM candidate cell; and the indication that the early UL synchronization was successful includes a further identifier associated with a further TCI state of the LTM candidate cell, based on which the early DL synchronization is performed.

15. The method of any of claims 1-14, wherein the single command is one of the following: a medium access control, MAC, control element, CE; a MAC protocol data unit, PDU; a physical DL control channel, PDCCH, order; a lean radio resource control, RRC, message; a layer-2 signaling message; or a layer- 1 signaling message.

16. The method of claim 15, wherein the MAC PDU includes first and second MAC CEs, the first MAC CE corresponds to a command to perform early UL synchronization, and the second MAC CE corresponds to a command to perform early DL synchronization.

17. The method of claim 15, wherein the single command is a MAC CE for early DL synchronization and one of the following indicates that the UE should also perform early UL synchronization in response to the MAC CE: a format of the MAC CE, a logical channel or logical channel group associated with the MAC CE, or content of a field in the MAC CE.

18. The method of claim 15, wherein the single command is a PDCCH order for early UL synchronization and one of the following indicates that the UE should also perform early DL synchronization in response to the PDCCH order: a format of the PDCCH order, or content of a field in the PDCCH order.

19. The method of any of claims 1-18, wherein the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single timing advance group, TAG, and the early UL synchronization is performed for all of the plurality of configured LTM candidate cells in the TAG.

20. A method for a radio access network, RAN, node configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs, the method comprising: sending (1110), to a UE via a source cell provided by the RAN node, a single command for early synchronization with an LTM candidate cell, wherein: the single command includes an identifier of the LTM candidate cell and an identifier associated with a transmission configuration indicator, TCI, state of the LTM candidate cell; and the single command facilitates both early uplink, UL, synchronization and early downlink, DL, synchronization of the UE with the LTM candidate cell.

21. The method of claim 20, wherein the identifier associated with the TCI state is a TCI state identifier, ID, such that early DL synchronization of the UE with the LTM candidate is based on UE activation of a TCI state, for the LTM candidate cell, that is identified by the TCI state ID.

22. The method of claim 20, wherein the identifier associated with the TCI state is an identifier of a reference signal, RS, of the LTM candidate cell, such that early DL synchronization of the UE with the LTM candidate is based on UE activation of a configured TCI state, for the LTM candidate cell, that has a quasi-colocation, QCL, source RS that matches or corresponds to the identified RS.

23. The method of claim 22, wherein the identifier of the RS is one of the following: a synchronization signal / PBCCH block, SSB, index; or a channel state information, CSI, RS resource identifier.

24. The method of any of claims 21-23, wherein early DL synchronization of the UE with the LTM candidate is further based on one of the following: a timer value sent to the UE in the single command, a timer value sent to the UE in a configuration for the LTM candidate cell, or a time alignment timer, TAT, value associated with early UL synchronization to the LTM candidate cell.

25. The method of any of claims 21-24, wherein the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single timing advance group, TAG, and early DL synchronization of the UE with the LTM candidate cell is further based on UE activation of UL or joint TCI states in other of the plurality of configured LTM candidate cells in the TAG.

26. The method of any of claims 20-25, wherein the identifier associated with the TCI state is a TCI state identifier, ID, and early UL synchronization of the UE with the LTM candidate cell is based on the following: a reference signal, RS, of the LTM candidate cell, that matches or corresponds to a quasicolocation, QCL, source RS for the TCI state identified by the TCI state ID; one or more random access, RA, parameters, for the LTM candidate cell, that are associated with the selected RS; and a RA preamble transmitted by the UE towards the LTM candidate cell in accordance with the RA parameters.

27. The method of any of claims 20-25, wherein the identifier associated with the TCI state is an identifier of a reference signal, RS, of the LTM candidate cell, and early UL synchronization of the UE with the LTM candidate cell is based on the following: one or more random access, RA, parameters, for the LTM candidate cell, that are associated with the identified RS; and a RA preamble transmitted by the UE towards the LTM candidate cell in accordance with the RA parameters.

28. The method of any of claims 26-27, wherein the RA parameters include one or more of the following: the RA preamble; and physical RA channel, PRACH, time / frequency resources.

29. The method of any of claims 26-28, wherein the early UL synchronization and the early DL synchronization of the UE are responsive to the single command.

30. The method of any of claims 26-28, wherein: the early UL synchronization of the UE is responsive to the single command and the method further comprises sending (1120) to the UE an indication that the early UL synchronization to the LTM candidate cell was successful; and the early DL synchronization of the UE is responsive to the indication.

31. The method of claim 30, wherein one or more of the following applies: the indication that the early UL synchronization was successful is a RA response to the RA preamble transmitted by the UE; the indication that the early UL synchronization was successful includes a TA value for the LTM candidate cell; and the indication that the early UL synchronization was successful includes a further identifier associated with a further TCI state of the LTM candidate cell, based on which the early DL synchronization is performed.

32. The method of any of claims 20-31, wherein the single command is one of the following: a medium access control, MAC, control element, CE; a MAC protocol data unit, PDU; a physical DL control channel, PDCCH, order; a lean radio resource control, RRC, message; a layer-2 signaling message; or a layer- 1 signaling message.

33. The method of claim 32, wherein the MAC PDU includes first and second MAC CEs, the first MAC CE corresponds to a command to perform early UL synchronization, and the second MAC CE corresponds to a command to perform early DL synchronization.

34. The method of claim 32, wherein the single command is a MAC CE for early DL synchronization and one of the following indicates that the UE should also perform early ULsynchronization in response to the MAC CE: a format of the MAC CE, a logical channel or logical channel group associated with the MAC CE, or content of a field in the MAC CE.

35. The method of claim 32, wherein the single command is a PDCCH order for early UL synchronization and one of the following indicates that the UE should also perform early DL synchronization in response to the PDCCH order: a format of the PDCCH order, or content of a field in the PDCCH order.

36. The method of any of claims 20-35, wherein the LTM candidate cell is one of a plurality of configured LTM candidate cells that are in a single timing advance group, TAG, and the early UL synchronization of the UE is with all of the plurality of configured LTM candidate cells in the TAG.

37. User equipment, UE (210, 510, 1212, 1300) configured for layer- l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1204), the UE comprising: communication interface circuitry (1312) configured to communicate with RAN nodes (100, 150, 220, 520, 1210, 1400, 1502); and processing circuitry (1302) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: receive, from a RAN node, a single command for early synchronization with an LTM candidate cell, wherein the single command includes an identifier of the LTM candidate cell and an identifier associated with a transmission configuration indicator, TCI, state of the LTM candidate cell; and based on the single command, perform early uplink, UL, synchronization and early downlink, DL, synchronization with the LTM candidate cell.

38. The UE of claim 37, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 2-19.

39. User equipment, UE (210, 510, 1212, 1300) configured for layer- l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1204), the UE being further configured to:receiving, from a RAN node (100, 150, 220, 520, 1210, 1400, 1502), a single command for early synchronization with an LTM candidate cell, wherein the single command includes an identifier of the LTM candidate cell and an identifier associated with a transmission configuration indicator, TCI, state of the LTM candidate cell; and based on the single command, performing early uplink, UL, synchronization and early downlink, DL, synchronization with the LTM candidate cell.

40. The UE of claim 39, being further configured to perform operations corresponding to the methods of any of claims 2-19.

41. Non-transitory, computer-readable medium (1310) storing computer-executable instructions that, when executed by processing circuitry (1302) of user equipment, UE (210, 510, 1212, 1300) configured for layer- 1 / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1204), configure the UE to perform operations corresponding to the methods of any of claims 1-19.

42. Computer program product (1314) comprising computer-executable instructions that, when executed by processing circuitry (1302) of user equipment, UE (210, 510, 1212, 1300) configured for layer- 1 / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1204), configure the UE to perform operations corresponding to the methods of any of claims 1-19.

43. Radio access network, RAN, node (100, 150, 220, 520, 1210, 1400, 1502) configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 510, 1212, 1300), the RAN node comprising: communication interface circuitry (1406, 1504) configured to communicate with UEs and with other RAN nodes; and processing circuitry (1402, 1504) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: send, to a UE via a source cell provided by the RAN node, a single command for early synchronization with an LTM candidate cell, wherein:the single command includes an identifier of the LTM candidate cell and an identifier associated with a transmission configuration indicator, TCI, state of the LTM candidate cell; and the single command facilitates both early uplink, UL, synchronization and early downlink, DL, synchronization of the UE with the LTM candidate cell.

44. The RAN node of claim 43, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 21-36.

45. Radio access network, RAN, node (100, 150, 220, 520, 1210, 1400, 1502) configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 510, 1212, 1300), the RAN node being further configured to: send, to a UE via a source cell provided by the RAN node, a single command for early synchronization with an LTM candidate cell, wherein: the single command includes an identifier of the LTM candidate cell and an identifier associated with a transmission configuration indicator, TCI, state of the LTM candidate cell; and the single command facilitates both early uplink, UL, synchronization and early downlink, DL, synchronization of the UE with the LTM candidate cell.

46. The RAN node of claim D3, being further configured to perform operations corresponding to the methods of any of claims 21-36.

47. Non-transitory, computer-readable medium (1404, 1504) storing computer-executable instructions that, when executed by processing circuitry (1402, 1504) of a radio access network, RAN, node (100, 150, 220, 520, 1210, 1400, 1502) configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 510, 1212, 1300), configure the RAN node to perform operations corresponding to the methods of any of claims 20-36.

48. Computer program product (1404a, 1504a) comprising computer-executable instructions that, when executed by processing circuitry (1402, 1504) of a radio access network, RAN, node (100, 150, 220, 520, 1210, 1400, 1502) configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 510, 1212, 1300), configure the RAN node to perform operations corresponding to the methods of any of claims 20-36.

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